The RenX Files: High idle problems

[Ecomike]

OK I don't think I am hasta, though it may sound like it at first. If you have any Renix experience please read this, as I think it lends a new perspective to an old, preplexing, frequent problem with high idles.

My old high idle Nemisis has returned uninvited. :(:bawl:

I have discovered that when I start the Jeep (87 Renix, 4.0), and if it idles to fast (recently started idling at 1000 to 2000 rpm again) and if it refuses to drop back down to normal, then if I disconnect the TPS sensor, the idle IAC control will finally operate ( there is about a 3 to 4 second delay) and lower the idle speed to a normal idle. :cool:

Then if I plug the TPS back in (re-connect the harness) the idle stays normal, unless I press the throttle again, (which I do not do because it eventually screws up the idle speed again if I do, not always right away, sometimes right away, sometimes it is a slow creep over minutes).

Then once I have gotten the IAC idle speed adjusted to the normal idle as I just described, I then unplug the IAC and drive the jeep. One of the interesting things is that once I have done this procedure the jeep runs great, including a roughly 30 to 50% increase in apparent horspower :cheers: when in gear that it has been lacking since I bought it 2.5 years ago.

I have tested the above problem, resolution procedure at least 8 times over the last week, and it is quite (100%) repeatable! Also if I disconnect the TPS and then press the throttle the engine dies right away.

Now it occures to me that the TPS must be working properly based on its flawless performance when the IAC is disconnected, and that it is still actually doing something control wise (data input to the ECU). It also must still be doing something, feeding good data to the ECU since it runs great when connected and dies when I press the accelerator if it is disconected!!!!! Right?????

Also, since the IAC works correctly when the TPS is disconnected, I must conclude that the IAC is also working when given the correct ECU instructions.

So what the hell could be causing this?????

To the best of my knowledge there are no battery, alternator, ground wire, or ignition problems (all of the ignition parts are new), and all the sensors have checked out recently and are fairly new.

I am looking for the non-obvious solutions.

I am thinking that either the ECU is getting faulty RPM data at some point, which makes no sense at all based on the way the engine runs, or it is giving faulty information to the IAC, but only when the TPS is connected and the throttle is pressed, or when the engine is first started. But why would it do this?

Why would it correct the idle speed, operating the IAC only after temporarily disconnecting the TPS????? Wiggling the connections at the IAC and the TPS has no effect on the system.

I eventually have to temporarily plug the IAC back in for real cold morning start ups, otherwise it tries to run and idle at about 250 rpm taking 20 minutes to warm up as a result on real cold morning first starts.

[boise49ers]

I frequeantly ( Couple times a year ) have to sray w-D in the connections on the Intake and snap them back togther. Works everytime. If you wash down your engine or get into Hi H20 areas they seem to start that crap.

[Ecomike]

I frequeantly ( Couple times a year ) have to sray w-D in the connections on the Intake and snap them back togther. Works everytime. If you wash down your engine or get into Hi H20 areas they seem to start that crap.

Which connections?

If you are talking electrical connections, that is not the problem here. They are good and solid. Also it is not a sticking IAC in this case, as it works if I disconnect the TPS.

[Ecomike]

OK it is "what if" time!

What if the voltage from the ECU to the TPS (circuit) temporarily dropped a little due to a poor connection somewhere else (other than the tps itself as I am sure it is good and tight) like the firewall bulk connector (I forget its name, C-102?), or the return volatge line from the TPS on its way back to the ECU?

Would that tell the ECU that the TPS was asking for more speed?????

Or tell it to slow down the idle even lower than normal????

What about the TPS's B wire ground that runs back to the ECU as a common sensor (C-4) ground for all the ECU sensors? If that ground was weakening occasionally what effect, if any, would that have on the idle speed?

[boise49ers]

Which connections?

If you are talking electrical connections, that is not the problem here. They are good and solid. Also it is not a sticking IAC in this case, as it works if I disconnect the TPS.
After reading deeper I figured that out. Sorry !

[Hella-XJ]

I have a 1990 XJ with the RenX motor and im haveing a Low(350-400rpm) idel problem any possibity it could be the same problem?
-Keep Jeepin

[blibra]

help same problem with 87 4.0! ! ! its driving me nuts. been trying to sort this for 3 days now. tried changing sensors, removed and cleaned tb . cleaned connections. when it happens it gets really slow and sluggish. idles 1500-2000rpm. it pushes and doesnt want to stop. jamming the throttle doesnt stop it. help! has anyone had any luck fix fixing this?

[MountainRhino]

I am having the same prob, but i am new to the jeep lifestyle so i really havnt done much to figure it out yet. just a lack of the necessary knowledge. sometimes its fine sometimes its really high, and sometimes its really low. no pattern and never under any certain conditions. i could use some of that troubleshooting help too.

[blibra]

tighten the intake manifold and exhaust manifold. this is most likely. . .this fixed everything. runs great now. maybe your tps is intermittent or you have a failing iac. almost all of the upper and lower bolts were loose on mine. one bolt underneath was half way off. i just had a vacuum leak from the intake manifold. good luck!

[boise49ers]

tighten the intake manifold and exhaust manifold. this is most likely. . .this fixed everything. runs great now. maybe your tps is intermittent or you have a failing iac. almost all of the upper and lower bolts were loose on mine. one bolt underneath was half way off. i just had a vacuum leak from the intake manifold. good luck!
Bet it runs and sounds a lot better. Those 2 bottom ones closest to the firewall suck to tighten.
:eek:

[blibra]

ya i feel stupid now being just some loose bolts. . . now it runs perfect besides the noisy power steering pump.

[MountainRhino]

good to know i will try thta

[Ecomike]

help same problem with 87 4.0! ! ! its driving me nuts. been trying to sort this for 3 days now. tried changing sensors, removed and cleaned tb . cleaned connections. when it happens it gets really slow and sluggish. idles 1500-2000rpm. it pushes and doesnt want to stop. jamming the throttle doesnt stop it. help! has anyone had any luck fix fixing this?

I don't feel the list bit sorry for your terribly long drawn out three days of exaperation :eek: chasing an idle speed problem, I have been chasing the ellusive multiple idle speed gremlins in the same jeep for 1.5 years now!
!!!1. So I hope that makes you feel better (or did it make it worse?) I have thought I had fixed mine a dozen or more times only to have it come back a month or two later. Each time something else seemed to fix it briefly.

OK, I see now reading your last post that you fixed yours! :clap: congratulations!!!!

[Ecomike]

Update by Ecomike:

On sunday, Feb. 4th, I worked on my oil filter adapter (another thread) While I had it out I was finally able to get to the ground wire mess on the passenger side of the engine block. What a mess, I ahd read about it and been told about it (5-90) but I had depended on the driver's side wire from the block to the firewall to fix the problem.


Bad idea. :lecture:

Turns out there about 4-5 other smaller wires that all attach to the same ground connection, including the battery. So even though I had a good ground from the engine to the firewall and to the battery negative post via the drivers side cable and the battery to the firwall run, all the electronic guys (ECU, ICM, TCM, and who knows whate else) grounds were loose, oily, dirty, oxidized....and they all are grounded at the rear passenger side of the engine block near the dipstick (not easy to get to, I had to remove the oil filter first).

So I cleaned up all the mini ground connections and reattached them. I also cleaned up the +12 Volt connections at the main start/run relay next to the battery + post.

So when I finished with that and the oil filter adapter project I reattached the IAC connector and the jeep ran great (idled perfectly, ran great, shifted great, even the 1 quart oil leak per 100 miles was gone:clap:) for 100 miles until tuesday evening when the fast idle gremlin (FIG, go figure right?) resurfaced again all of sudden after 5 to 6 hours of driving and multiple trips.

I am going to recheck the TPS voltage next to see if the improved controls ground affected the idle possition voltage.

For now I am going back to disconnecting the IAC controler connection with it set for an average idle of about 450 rpm cold, 600 rpm warm and 750 rpm hot in park.

[Ecomike]

To all those who claim to be a Renix expert here (and to those who just are Renix experts, even if they do not claim to be one),
I have not received a single answer to my oringinal question in this post!!!!!!!

Have I stumped the experts??????? :rattle:

Please help!

[langer1]

Did anyone replace the IAC relay?

[clunk]

I would just say your TPS is wonky. Didn't you post about a shifting problem a while back? It seems the TPS would cause the same idle problems you are having now, as well as the shfiting problem.
I wouldn't be surprised if, when you cleaned the grounds next to the oil dipstick that you got a higher voltage on the TPS, and this threw off your adjustments. Go back, test the voltage and see if it changed anything. If it did, make the necessary adjustments. I've been meaning to get around to cleaning those ground wires but they are a bit of a pain to get to so I have been putting it off.

[Flash]

I'm a fan of the Renix but have just began to learn about then,...........is there any grounds for the computer that attach to the body(under the dash?:dunno: )

What is it, that's the same every time it acts up,............just after a rain, after a long drive, only when ya baby it, or when you drive it like ya stoled it, full tank of gas.... next to empty, when the defrost is on, when the a.c. ins one EXC.:eyes:

ask your self these question and more when it acts up. If we can find something that is there every time it act's up then we have a path or a direction to go.


Flash.

[Ecomike]

Did anyone replace the IAC relay?

NO! Is there a relay between it and the IAC that I am not aware of???????????? Or are you asking about the IAC itself. I have tried, replaced the IAC with new ones twice.

If it was a relay why would the IAC operate 3 seconds later and reset the idle speed to the proper idle speed for the current operating conditions (such as air and coolant temp, etc) when I disconnect the TPS while the engine is running?

Then when I reconnect the TPS it stays at that correct idle speed until sometime later (totally variable, no pattern*) when I start driving it (operating the accelator*) again. Sometimes the idle speed stays normal for a while after the TPS disconnect fix, other times it acts right up after operating the TPS-throttle again.

The TPS is also new (less than 12 months old, with less than 1500 miles on it), and keep in mind that I recently had one of the longest stretches of proper idle operation (500 miles, 4 weeks) since I started having idle problems 1.5 years ago.

But back to your question, I thoroughly cleaned all the under the hood relay contacts and harness connector contacts as best as I could. The harness (female) connectors are hard to get at. I may try wiggling them the next time the idle wanders off again!!!!!

[Ecomike]

Did anyone replace the IAC relay?

Were you referring to the power latch relay that sets the IAC position using a timed power down delay after the engine is powered down?

If yes, I do not know for sure, I have replaced on or two of the small square plug-in relays, and swapped some around to test them so I am not sure. I have cleaned the male pins on all the under the hood relays including the power latch relay if it is under the hood (?).

[Ecomike]

I would just say your TPS is wonky. Didn't you post about a shifting problem a while back? It seems the TPS would cause the same idle problems you are having now, as well as the shfiting problem.
I wouldn't be surprised if, when you cleaned the grounds next to the oil dipstick that you got a higher voltage on the TPS, and this threw off your adjustments. Go back, test the voltage and see if it changed anything. If it did, make the necessary adjustments. I've been meaning to get around to cleaning those ground wires but they are a bit of a pain to get to so I have been putting it off.
Yes to the shifting problem post. I solved it recently, I think (can't these things too loud as there are jeeps nearby, :laugh2:) with the transmission to throttle body cable adjustment. That transmission throttle body cable adjustment made a HUGE difference:D in the shift points, power, etc.

I agree my fixing the ground connections, probably unfixed the 0.80 volt idle setting on the TPS!:tears: But what is wierd is the malfunctioning idle (trying to run too fast) went away for 2 days and 100 miles after I fixed those ground connections, and then just returned after two days of flawless operation.:wierd:

I understand the putting it off on cleaning that ground area, it is a pain. Planed it for 3 months myself before I got a ROUNDTOIT!:roll:

Thanks for feedback. I am planning to test and adjust the TPS idle back to 0.80 volts this weekend, if not sooner. At least that is easy to do.

[Ecomike]

I'm a fan of the Renix but have just began to learn about then,...........is there any grounds for the computer that attach to the body(under the dash?:dunno: )

What is it, that's the same every time it acts up,............just after a rain, after a long drive, only when ya baby it, or when you drive it like ya stoled it, full tank of gas.... next to empty, when the defrost is on, when the a.c. ins one EXC.:eyes:

ask your self these question and more when it acts up. If we can find something that is there every time it act's up then we have a path or a direction to go.


Flash.
Flash,

So far I have resisted the temptation (not hard to do) to mess with the ECU and the wiring under the dash near the steering column. So far the problems (oil, dirt, corrosion, heat, rotting harness problems) under the hood were far worse than any inside under the dash based on my visual inspections. I am just about finished cleaning up and fixing the mess that was under the hood, so I will be pulling the dash and doing some work behind the dash as soon as the cold weather ends here partly to replace the radio, antenna and antenna wire and to clean the ECU and ECU harness connections.

I did test the ground connections at the D1 (ECU ground at pin 3) and D2 (Sensor ground at pin 8) diagnostic connectors on the passenger side fender under the hood a few months ago and they tested well under 1 ohm.

The only similarities when it acts up, is that is totally RANDOM!!!!!!!:rattle:One day it will do it cold. The next day it does it hot, the next day at start up, the next day only after a long drive, then on a rainy day, then not on a rainy day, then it won't do it for days, hot or cold.....absolutely no consistent pattern at all over the long term. It might show a pattern for few hours or days, and then it will change or go away for a day, week, ....

AH HA, there is a pattern after all! It only does it when the engine is running!!! :rof::rof: :laugh2: :D

[Flash]

:D Well theres some good news.... have ya checked the ground D1 D2 when it acting up?(I can tell ya already know more about the situation at had than i, but two...or more, heads, can generally keep ya going down the right path

It really sounds like a ground issue to me:dunno:
maybe a ground probem.........do the IAC, step up motor and tps exc get there ground from the ECM or a chassis ground?

It to bad ya didn't have a nether ECM that ya could swap out!

What about the intake bolts being loose like some mentioned........Hmmmm that wouldn't fix its self when you unplugged and replugged the sensor.:twak:

Flash.

Flash,

So far I have resisted the temptation (not hard to do) to mess with the ECU and the wiring under the dash near the steering column. So far the problems (oil, dirt, corrosion, heat, rotting harness problems) under the hood were far worse than any inside under the dash based on my visual inspections. I am just about finished cleaning up and fixing the mess that was under the hood, so I will be pulling the dash and doing some work behind the dash as soon as the cold weather ends here partly to replace the radio, antenna and antenna wire and to clean the ECU and ECU harness connections.

I did test the ground connections at the D1 (ECU ground at pin 3) and D2 (Sensor ground at pin 8) diagnostic connectors on the passenger side fender under the hood a few months ago and they tested well under 1 ohm.

The only similarities when it acts up, is that is totally RANDOM!!!!!!!:rattle:One day it will do it cold. The next day it does it hot, the next day at start up, the next day only after a long drive, then on a rainy day, then not on a rainy day, then it won't do it for days, hot or cold.....absolutely no consistent pattern at all over the long term. It might show a pattern for few hours or days, and then it will change or go away for a day, week, ....

AH HA, there is a pattern after all! It only does it when the engine is running!!! :rof::rof: :laugh2: :D

[Ecomike]

Flash,

" :D Well theres some good news.... have ya checked the ground D1 D2 when it acted up? Its to bad ya didn't have a spare ECM that ya could swap out!

What about the intake bolts being loose like some mentioned........Hmmmm that wouldn't fix itself when you unplugged and replugged the sensor.:twak:"

Now your catching on:yelclap:. That's right most vacuum leaks do not fix themselves. I have 2 spare ECMs, but I have not tried them, since bad ECMs :badpc: don't fix themselves either, LOL. I agree it sounds like an intermittent ground, but I am running out grounds, and other wiring harness connections to clean up and restore.

I am just about ready to start looking for the muffler bearings to see if they might be causing the problem.

I will try checking the D1 and D2 ground connections the next time the idle takes off the runway.

[Flash]

Here is a thought, add a good point! checking Resistance can fool ya into thinking a bad wire is good!

let me try and exlplain..................if you take a length of wire and strip a section of it and brake every strand but...1 and run a ohm reading it will pass with flying colors but try to send voltage w/ a load thru that same wire and you have a vary low voltage at the ether end.

This is how I test a questionable section of wire or wires. The first thing you have to do is isolate the wire(wiring schematic will help here a lot) so there is no way that it can get to the computer.....which would ruin it!!!!!!

OK now that you now there is no power or ground going thru the wire you trying to test say...a....D1 pin 3 and it destination(remove form the computer and remove from the ground or sensor) now put 12 volt at one side of it and a load to ground on the eater side did it flow the voltage thru it?????

This is the testing apparatus that i made for this test! get a tail light socket and an 1157,2057 exc and put the bulb in the socket attach enough wire to It so that you can go from the bat. to one end of the wire and then ground the aether end of the wire........if there is only one strand of wire in that wire some wheres, the light bulb WILL NOT light!
Its much better then putting power on one side and checking with a volt meter on the aether side(12 volts will travel thru that same sing strand of wire as the ohm meter did but the 1157 (Park brake light bulb) bulb will not!
Becouse it will cause a amperage to be pushed thru the wire.

Just to clarify the strand ..........there is many strands that make up one wire and then it is cover in plastic coating......but you know what .....right!


dose that make sence to you???


Flash.

[Ecomike]

eferHere is a thought, add a good point! checking Resistance can fool ya into thinking a bad wire is good!

let me try and exlplain..................if you take a length of wire and strip a section of it and brake every strand but...1 and run a ohm reading it will pass with flying colors but try to send voltage w/ a load thru that same wire and you have a vary low voltage at the ether end.

This is how I test a questionable section of wire or wires. The first thing you have to do is isolate the wire(wiring schematic will help here a lot) so there is no way that it can get to the computer.....which would ruin it!!!!!!

OK now that you now there is no power or ground going thru the wire you trying to test say...a....D1 pin 3 and it destination(remove form the computer and remove from the ground or sensor) now put 12 volt at one side of it and a load to ground on the eater side did it flow the voltage thru it?????

This is the testing apparatus that i made for this test! get a tail light socket and an 1157,2057 exc and put the bulb in the socket attach enough wire to It so that you can go from the bat. to one end of the wire and then ground the aether end of the wire........if there is only one strand of wire in that wire some wheres, the light bulb WILL NOT light!
Its much better then putting power on one side and checking with a volt meter on the aether side(12 volts will travel thru that same sing strand of wire as the ohm meter did but the 1157 (Park brake light bulb) bulb will not!
Becouse it will cause a amperage to be pushed thru the wire.

Just to clarify the strand ..........there is many strands that make up one wire and then it is cover in plastic coating......but you know what .....right!


dose that make sence to you???


Flash.

Yes, I understand what you are doing. I prefer to check the ground resistance (and thus the entire wire integretty and connectors) from places like the D connectors (or the valve cover/engine block and firewall) to the battery negative post while the engine is running, by testing on the volts scale.

If there is voltage (over say 0.02 volts) between the D connector ground and the battery ground then that would indicate to me a poor ground. If the voltage is 0.02 volts or less than I consider the ground to be good.

The test can be run with various hardware running like head lights, radio, a/c blower on high to load up the grounds as much as possible.

The test can also be run on the ohms scale, but I trust the ohm reading better with the power off since stray voltages can affect the ohms reading when the engine is running. The voltage test procedure works with all the devices powered on in a dynamic ground load test on the ground wires sort of way.

Your procedure is OK for isolating a specific wireground problem, but I have yet to find further evidence of a ground problem to test for. The next time the gremlin pops up, I will test the voltage from the D connectors to the battery ground for sure while it is malfunctioning!
That is something I have not done before!!! That could prove interesting.:D

I will also check the TPS idle voltage at the same time (during the idle speed malfunction). That could be interesting as well.

[langer1]

Yes the power-latch relay. Listen when you turn the key off, you should hear a buzzing noise every time. If the IAC don't reset to (0) position every time, the next start will be on High idle.

The only way the computer knows the position of the IAC is it counts up from zero. so it must be reset to zero every time.

[clunk]

Yes the power-latch relay. Listen when you turn the key off, you should hear a buzzing noise every time. If the IAC don't reset to (0) position every time, the next start will be on High idle.

The only way the computer knows the position of the IAC is it counts up from zero. so it must be reset to zero every time.

you mean the "keys in ignition, engine off" buzzing? Mine only does that intermittently, never associated it with any sort of high idle though.

[langer1]

You have to be under the hood to hear it, it's not the Chime buzzer that I'm talking about.

It's actually more of a whine or whistling sound than a buzz.

[Ecomike]

You have to be under the hood to hear it, it's not the Chime buzzer that I'm talking about.

It's actually more of a whine or whistling sound than a buzz.

Chime Buzzer! It must be dead. :dunno:


So which relay is it? :dunno: Any pictures?

Is it the "B+ power latch relay" second from the rear on the pasenger side along the fender, part of a group of 4 relays near the ignition coil?

I have a diag showing the first relay (nearest the firewall) as the A/C clutch, second relay is the B+ power latch relay, then the fuel pump relay, then the oxygen sensor relay (runs the heater in the O2 sensor). Four cube style relays in a row.

[Ecomike]

Langer 1,

I could not hear the sound you described (relay or IAC motor buzz or whine) but a second person was able to feel the B+ latch relay working for 3 seconds after I shut the engine off.

I changed the already new relay (B+ latch relay) with a newer one. Made no difference.

Then I tested the TPS voltage (C+ to B ground) which I had calibrated weeks ago to 0.80 volts at idle. It was up to 1.07 volts!!!!! An increase of 0.27 volts or about a 1/3 increase over spec.

So fixing and cleaning the multiwire sensor ground connections at the engine block / dip stick location last weekend did affect the TPS calibration afterall!!!!!

I recalibrated the TPS idle voltage to 0.79 volts (closest I could get at the time, I was in a hurry).

It is now (at least so far) idling normally again!!!!party1:

It was trying to idle at 2,000 (cold) to 2,500 rpm (hot):scared: before I recalibrated the TPS.

Since the correct idle speed is 600 rpm that means it was 1400 to 1900 rpm faster than normal. If I divide 1900 RPM by 0.27 volts, times 100,
[(1900/.27)*100]
I get 70.37 rpm for every 0.01 volt error in the TPS idle position voltage calibration! (assuming it is linear).

That means an electrical connection error (poor ground) causing a + 0.01 volt error will cause the idle speed to be increased by 70 rpm. A TPS voltage error of + 0.10 volts would cause a 704 rpm increase error. That is assuming that the Renix ECU is outputing a linear RPM speed increase to the TPS voltage signal. If it is non-linear we would need to test several voltages and RPMs to plot it out. Not sure it is worth the trouble.

My point in the calculations above is to demonstrate that the TPS calibration and the system grounds are extreemly sensitive to small variations as low as 0.01 volts!!!!!!!!

An error of 0.05 volts (350 rpm) would become quite noticable. Especially if the error was -0.05 volts (.75 volts net at idle) and the engine was trying to idle at 250 rpm!!!!!:gag:

I know that others including 5-90 :wave: preach :lecture: the importance of good grounds on the Renix Jeeps:worship:, but these measurements I just made put the quality of the required ground into perspective:eek:, at least for me!

Stated another way, the system runs at about 14 volts. A .01 volt error in a 14.00 volt system is four significant figures of precision, or a 0.1 % error. Many systems only have measurement precision to 2 decimal places (like a measuring beaker in a lab, typically +/- 5% volume).

No wonder we all have so much fun :woohoo:with the idles on these 20 year old jeeps!

By the way, if the TPS-ECU is that sensitive to a 0.01 volt variation, I suspect that many CPS have been replaced on jeeps when the real problem was the ground!!!!!! I suspect the CPS input to the ECU is even more sensitive to a poor ground, week or dirty electrical contacts than even the TPS!!!!

[Greg Smith]

I have a 1990 XJ with the RenX motor and im haveing a Low(350-400rpm) idel problem any possibity it could be the same problem?
-Keep Jeepin

Disco and reconnect the crank position sensor connector. This connector often losens up internally creating resistance and can cause no start or low idle. The pre 91 have a cps that self generates only up to 1 volt so any resistance in this connector can cause problems. I eventually replaced the connector w. a screw together connector to cure this problem. Good Luck Greg

[Ecomike]

Disco and reconnect the crank position sensor connector. This connector often losens up internally creating resistance and can cause no start or low idle. The pre 91 have a cps that self generates only up to 1 volt so any resistance in this connector can cause problems. I eventually replaced the connector w. a screw together connector to cure this problem. Good Luck Greg

Starting problems yes, most definately, but I doubt that a CPS problem can cause a low idle only. Possibly a rough idle?

[Dundy]

I have an 87 Xj with the Renix (240,000 miles) and the high-idle problem happens for me also. IT only happens when i start it up in the cold and don't let it warm up. After a little while (10 or 15 minutes) the idle starts to drop back down. Once it is done with that it idles at a nice 550 rpms and runs like a top. However, when i let it warm up for 15 minutes the problem is non-existant.

Dundy

[Ecomike]

I have an 87 Xj with the Renix (240,000 miles) and the high-idle problem happens for me also. IT only happens when i start it up in the cold and don't let it warm up. After a little while (10 or 15 minutes) the idle starts to drop back down. Once it is done with that it idles at a nice 550 rpms and runs like a top. However, when i let it warm up for 15 minutes the problem is non-existant.

Dundy

Try cleaning all the ground connections at the battery, the engine block near the oil dip stick, passenger side and the 2 firewall to engine block grounds. One is on the drivers side valve cover bolt at the rear and the 2nd is from the oil dip stick to the firewall. Then recalibrate the TPS idle voltage +C to B ground at +0.80 volts with ignition on but engine off (do not start it, but with ignition power in the on postion).

[Greg Smith]

Starting problems yes, most definitely, but I doubt that a CPS problem can cause a low idle only. Possibly a rough idle?


Low idle is often rougher! Just my experience with the CPS after owning and working on my renix sys XJ since 1989!

Also my experience with high idle has been vacuum leaks especially due to loose intake manifold bolts and loose or cracked vacum lines to the bottom of the throttle body. A sticking or dirty IAC can cause it also. The IAC plunger and the seat it presses against needs to be clean for a good seal after fully warm up or else you will get leakage and a higher idle.

For spiking idle at start up at 2000 to 3000 which can be stopped on occasion by restarting or discoing and reconnecting the TPS, it is usually the sign of a TPS going bad also can cause your auto tranny to not shift or do so erratically. This is per my long time personal experience and info from jeep techs. Solution is usually a new TPS installed and properly adjusted. Of course all grounds and connectors involved should be checked to eliminate corrosion and resistance.

In my view your problems are likely a bad TPS. Also my fsm for my 89 says to adjust the tps to between .825-.835 volts. Good Luck.

:repair: Greg

[Greg Smith]

I have an 87 Xj with the Renix (240,000 miles) and the high-idle problem happens for me also. IT only happens when i start it up in the cold and don't let it warm up. After a little while (10 or 15 minutes) the idle starts to drop back down. Once it is done with that it idles at a nice 550 rpms and runs like a top. However, when i let it warm up for 15 minutes the problem is non-existant.

Dundy


The 87s and perhaps 88s have a very troublesome master connector on the bulkhead through which many sensors connect including the cps and perhaps tps. The anti corrosion gel inside goes bad and allows corrosion on the connectors inside. Clean and and relube w. dielectric grease every couple of yrs. And make sure the connectors give a tight fit and check for resistance through the connector. Resistance is bad! Jeep eliminated this connector for a reason. Some have soldered the wires together for the same reason. Greg

[Ecomike]

Well after a week of completely flawless idle operation I found a new way to get an unwanted high idle with my 87 Renix! :gonnablow

Then I discovered that the Non-OEM floor matt had shifted up under the gas peddle :shocked: when I climbed in the jeep. :banghead:

Needless to say the floor mat is about to get trimmed and possibly super glued in place!:yap:

Of course I am now wondering if this has not happend to me before????:exclamati

[jeepler]

hey how ar u i have an xj and im getting some of these same problems with my idel when its cold it idels fine when it warms up it idels at 1100 rpm but when unplug my tps it still runs but when i give it gas it back fires through the intake so im thinking it might be a iac. but i just got the jeep a month a go and i dont know to much about them. ohh and i also just put a new tps on mine and adjusted it but i get the same thing. dont think this helps u much but thought i should put it out there for people to see and maybe this can be figured out.

[Ecomike]

hey how ar u i have an xj and im getting some of these same problems with my idel when its cold it idels fine when it warms up it idels at 1100 rpm but when unplug my tps it still runs but when i give it gas it back fires through the intake so im thinking it might be a iac. but i just got the jeep a month a go and i dont know to much about them. ohh and i also just put a new tps on mine and adjusted it but i get the same thing. dont think this helps u much but thought i should put it out there for people to see and maybe this can be figured out.

First try cleaning all the ground connections. Start at the battery, then the engine block near the oil dip stick on the the passenger side and then the 2 firewall to engine block grounds right and left sides. One is on the drivers side valve cover bolt at the rear and the 2nd is from the oil dip stick to the firewall. Then recalibrate the TPS idle voltage +C to B ground at +0.80 to .82 volts with the ignition on but the engine off (do not start it, but with ignition power in the on postion).

When done you should read less than 1 ohm between the battery ground post, engine block and firewall with the ignition off.

What year is your Jeep?

[jeepler]

its a 1990

[Ecomike]

its a 1990

The you definately need to get serious about agressively cleaning all the ground wire connectors under the hood that I mentioned below including the connection points (engine block bolt areas, firewall bolt areas, and the battery posts and clamps as well). Do them all before spend a dime on any parts!

Wish I had done this two years ago before I spent $$$$$$s on parts and #####hrs working on my various idle problems.......

[jeepler]

hey i checked all the grounds and every thing is ok and still have the same problem i also cleaned the iac. same thing

[Flash]

NOT trying to harp on you..........but you, REALLY need to go the first of this post and read it. there is grate info here, and in the end you will understand why the ground is the most importunate place to start and get right!

Appearances can be deceiving and these grounds are no exception to the rule!


Flash.

[waggy]

i have had problems like this before , some have been sensors gon to the poop house ,but the ones that were the hardest to figure out where the ones where the sensors were fine . one of the first ones was my egr aws leaking air in causing a high idle . that one was actually easy to find . the one that was the bigest PITA was the TB butterfly was oblonged and wasent shutting properly . i would reccomend looking at the TB for wear inside the bore .even check how tight the TB is , could be a bad seal between the intake and TB . good luck

[falcon556]

I frequeantly ( Couple times a year ) have to sray w-D in the connections on the Intake and snap them back togther. Works everytime. If you wash down your engine or get into Hi H20 areas they seem to start that crap.

I had the exact same problem and cured it the exact same way.

[Ecomike]

Also my fsm for my 89 says to adjust the tps to between .825-.835 volts. Good Luck.

:repair: Greg

My Renix FSM, 1987, says "About 0.80 volts" so after a long period of trouble free "Normal" idle I decided to run an experiment.

I reset the idle voltage from 0.80 to 0.82 volts. Started the jeep and the idle jumped up to about 1250 rpm.

I unplugged the TPS, let the idle drop, then plugged it back in and the idle stayed normal. I turned it off and restarted it and it still ran a bit a high, but only for a few minutes at about 850 rpm. Once it warmed up the idle droped from about 850 rpm to about 650 rpm (normal).

I left it at 0.82 volts for the past week, ran a long highway trip and several daily short stop and go trips, let it get hot.....and so far it is still idling normally at the same hot idle speed that it idled at when I had it set at 0.80 volts!!!!

[Ecomike]

Something real interesting happened yesterday. First, I have had no idle problems since my last post.

Yesterday, I left the power on with engine off for about 20 minutes, playing the radio. When I restarted the Jeep the idle was hung up at about 1200 rpm. I turned it off 5 seconds, then on 5 seconds, then started it, idle was 1200 rpm. Gave it gas and the idle stuck at 1,500 rpm. :cry:

I disconnected the TPS, no effect. Disconnected the IAC and reconected the IAC, no effect. Reconnected the TPS, no effect.

Then I started the jeep with the TPS disconnected. The ilde dropped to 1100 rpm. :rof:Cycled the engine off 5 seconds, then back on 5 seconds then started it, Idle dropped to 750 RPM and held. :rof:Idle in drive was 600 rpm. No more idle probelsm since.

I am convinced the problem started with the Renix computer not liking the engine power being left on while the engine itself was off for 20 minutes! I am also further convinced that even though Renix does not store codes or allow code or operating data history retrieval, it is storing some operating history in some limited non volatile memory (I have found FSM statements that back that up), that affects things like Idle IAC settings until the system has been cycled several times to replace older operating data with newer data. I do not think disconnecting the battery on a Renix removes that stored operating data history.

So what worked was disconnecting the TPS before starting the jeep. Starting it with power on for 5 seconds, start-run for 60 seconds, power off for 5 seconds, then repeating the procedure once. Then reconnecting the TPS and restarting the jeep. That fixed the problem this time! (but only because the parts and grounds are still good!).

[joshv98xj]

I've got a question to add onto this discussion. Just so you know, I've read the whole thing, so I'm gonna take a look at cleaning all those connections tomorrow. Where specifically is the ground by the oil filter? That wasn't all that clear. But that's not my real question.

My high idle problem is as follows: When I start the truck when it's cold, it will idle at a relatively normal rate, sub-1000rpms. But as it warms up, the idle will increase directly corresponding to the temperature gauge rising. The idle will rise until the temp reaches normal, roughly 205, at which point the engine is idling at about 2200!

I have not pulled any of the sensors while it was running, but I did replace the the IAC with another one I had laying around, no effect. I removed and cleaned the TB and IAC, no effect.

Any ideas that would cause this direct correspondance other than cleaning those grounds?

[Ecomike]

The ECU sees a complete circuit for each sensor which includes the ground. If the ground conections are ever so slightly loose, dirty and oxidized the ground connection resistance changes as the engine warms up and cools. This results in a changing TPS signal, voltage to the ECU that makes the ECU think you have your foot on the gas pedal.

There are about 5 grounds all stacked under one bolt behind the oil filter adapter and next to the oil dip stick holder.

It could also be a temperature related leak that opens up as the engine heats up at the intake manifold.

Oh, and by the way, I have had no further idle problems since my last post here 3 weeks ago.:D

[falcon556]

There are about 5 grounds all stacked under one bolt behind the oil filter adapter and next to the oil dip stick holder.



I would like to add something that applies to connections like that, when you have a stack of grounds, it is important that they are clean corrosion free and tight otherwise they can start completing the circuit for each other giving all kinds of erratic results. ust general info, I don't think it applies here.

[joshv98xj]

Today, it was idling at up to 2700!!! So I unplugged both the IAC and the TPS, separately. No effect. I cleaned the ground by the oil filter. It was pretty gunky, and the ground from the battery was totally shot. So I replaced it. No effect. So I checked the intake manifold bolts, one of them was loose to the point I could spin it with my fingers, and a few others I tightened up a bit more with the wrench. Now my idle is at about 1750, which I consider a victory. At least it doesn't sound like it's screaming. What else should I check? I'm not that experienced with my multimeter, so how do I actually check to see if the IAC and the TPS are working?

[falcon556]

What else should I check?

Check for more vacuum leaks. It may be your only problem. Check everything.
I used to use a certain carburator cleaner years ago. I don't remember which one.
When I sprayed a leak area it would show an rpm change and smoke in the exhaust.
The intake gasket is not that hard to replace.

[Ecomike]

Based on your findings I would continue to suspect some more vacuum leaks, or intake manifold leaks. Any brand aerosol carburator cleaner should work just spray it at the joints betwen the engine block and intake manifold while the engine is running. IF you get any RPM change you found another leak location.

But it sounds like you have made a lot of progress.

because have fixed some bad grounds, you now need to back probe the TPS sensor connection at pin B and Pin C, they are marked on the connector, set the multi meter to DC volts, use a scale between 2 and 10 volts (set the selector if it is not autoranging to 2 to 10 volt scale), insert the probes into the proper spots on the meter for DC volts, then insert the probes into the back side of the TPS sensor connector while it is connected to the wiring harness until you make elctrical contact and get a voltage reading. Lossen the two screws that hold the TPS sensor in place, rotate the sensor until you read about 0.82 volts on your meter, then retighten the screws holding the TPS in place.

The intake manifold leak masked a smaller idle speed issue from the dirty grounds, now that some of the intake leaks are fixed and idel has dropped and some of the grounds are restored (You still need to clean the firewall grounds!) you need to recalibrate the TPS.

Then try starting and running for say 3 minutes, and shuting down the engine for about 1 minute, 3 times in a row. Then let us know what is happening idle wise after that.

[joshv98xj]

Okay, so I tried the carb cleaner around the manifolds, and I really didn't get much of any change in the RPM's. Would I be looking for an increase or a decrease in RPM's? The only change I thought I heard was a bit of an increase, but I think that may have been due to the initial startup of the engine, as it searched for the idle level.

Next I tried cleaning a few of the other grounds I could find. I cleaned a few on the fenderwalls, but I didn't see any on the firewall, maybe I need to look harder? The engine was hot at the time, so I didn't really feel like sticking my hands around everywhere.

I tried unplugging the IAC and the TPS again, separately, with no effect? Does that mean they are working or not working? I was able to set the TPS voltage reading at 0.84, I was pleased I got that close. That really didn't alter the idle though; a small amount, but not much.

I looked around for more vacuum leaks, but didn't find anything noticeably loose or absent. Just to add to the info, I did swap out my vacuum disconnect D30 for a late model, non-disco D30. I just plugged the lines running to the shift fork motor, is that okay or could that be my problem? How should I plug or re-rout them?

Lastly, I did the 3 min/1 min thing a few times, then I drove home about 10 minutes, with no noticeable change. I think I'm at a pretty steady 1700, which, from yesterday is about another 50-100 rpm's, so I think I'm still making a little progress.

Could something in my EGR system be the cause of all of this? I'm sure the answer is probably yes, which is why there is never an easy answer to these high idle questions. Anyway, how would i go about testing any of those components? I don't have a vacuum guage/meter or pump.

[old_man]

There is a large braided ground wire running from one of the drivers side headbolts back to the firewall just to the center from the MAP sensor.

[falcon556]

I looked around for more vacuum leaks, but didn't find anything noticeably loose or absent. Just to add to the info, I did swap out my vacuum disconnect D30 for a late model, non-disco D30. I just plugged the lines running to the shift fork motor, is that okay or could that be my problem? How should I plug or re-rout them?
Try plugging vacuum lines at the sourse. Disconnect and plug the line that goes to the canister behind the bumper, the Cruise servo etc.

[Flash]

I've got a question to add onto this discussion. Just so you know, I've read the whole thing, so I'm gonna take a look at cleaning all those connections tomorrow. Where specifically is the ground by the oil filter? That wasn't all that clear. But that's not my real question.

My high idle problem is as follows: When I start the truck when it's cold, it will idle at a relatively normal rate, sub-1000rpms. But as it warms up, the idle will increase directly corresponding to the temperature gauge rising. The idle will rise until the temp reaches normal, roughly 205, at which point the engine is idling at about 2200!

I have not pulled any of the sensors while it was running, but I did replace the the IAC with another one I had laying around, no effect. I removed and cleaned the TB and IAC, no effect.

Any ideas that would cause this direct correspondance other than cleaning those grounds?


I two have read all of this thread, and have been fallowing Ecomike trial and Quest for the cure:worship:

My 89 XJ has had the heated (as temp go's up....RPM go's up!) problem for awhile. After reading here a fue weeks a go, i got my meter and found .4 oms of Resistance.

Check it a couple of days a go, when it was hot and idling high.

I had 8.0 oms of Resistance, took a knife and remove the insulation next to the battery and there was still about 3.
This puzzled me because there was no corrosion on the post or the terminal,
On the block side it was oil soaked.

I started twisting and moving the negative battery cable around and re checking the resisince.....it when up, way up, 34 oms of Resistance.

At this point lunch was over and i had to park my jeep.

Started it and it rev higher then it has ever been before. it had to be Turing 3,000 at least! (I have no tach)
when i when to go home that night, idles just fine and by the time i got home it was at is normal high idle.

Bought a new cable, carefully remove the stud in the block and clean and dielectric greased every thing.
Tightened it all up and it has not had a high idle every sense.

It's really nice to turn the key off, and not have to Wait for the eng to stop, before letting out the clutch!

Flash.

[Ecomike]

I didn't see any on the firewall, maybe I need to look harder?

Just to add to the info, I did swap out my vacuum disconnect D30 for a late model, non-disco D30. I just plugged the lines running to the shift fork motor, is that okay or could that be my problem? How should I plug or re-rout them?

Could something in my EGR system be the cause of all of this?

There should be two on the rear firewall, the one old_man describes below is on the drivers side at the rear of the head on the engine block. The other is a continuation of the battery ground from the battery to the engine block near the dipstick, it should continue up and over to the firewall from near the dip stick on the engine block, passenger side. Is it missing???? Are they missing????

You got me on the D30 stuff, some one else will have to answer that one, but if it is leaking, sucking air it is adding to your idle speed problem.

EGR, I think the answer may be yes, if the EGR diaphragm is bad it may be possible for it introduce air into the vacuum line, but I doubt it. I think bad EGRs cause other idle problems. Just temporarily disconnect and plug the vac line to the EGR to test it. It is that simple.:D

[Evil88]

Damn, I love my DRB-II.

To everyone check your wiring. I have found that most all of my problems were electrical (wiring) not the actual sensors.

[joshv98xj]

There should be two on the rear firewall, the one old_man describes below is on the drivers side at the rear of the head on the engine block. The other is a continuation of the battery ground from the battery to the engine block near the dipstick, it should continue up and over to the firewall from near the dip stick on the engine block, passenger side. Is it missing???? Are they missing????

Okay, here's what I got. First off, here's the battery cable I replaced!

Secondly, I don't really know if I'm missing anything, so I'll tell you what I've got. At the ground by the dipstick, there is the HD wire coming from the battery, and there are two small wires coming from the harness, I didn't pull the harness apart to see where they go. The wire from the battery dead ends at the ground bolt. I didn't know the big braided wire on the driver's side was a ground, I guess because it doesn't go anywhere- just from the head bolt to the firewall, nothing else. I found one small ground under the coolant resivoir, and that's about it.

I didn't get a chance to clean that ground or the braided one just yet. Here's a few pics of what I've got, let me know if you see something wrong or missing.

How do I begin to diagnose or trace a vacuum leak problem? Is there any method to it?
http://i117.photobucket.com/albums/o65/joshv98xj/IMG_1096.jpg

http://i117.photobucket.com/albums/o65/joshv98xj/IMG_1099.jpg

http://i117.photobucket.com/albums/o65/joshv98xj/IMG_1102.jpg

[89xj]

most obviuos way to check for a vacuum leak is that you can hear it. other way is to trace your lines and look for crackes and spray wd40 on the lines and listen for increase in rpm.

also, when you found loose manifold bolts and tightened them, did you look for missing ones. i know on my 89 i had a few loose and was completely missing one.

oh, where are you located near philly? im in delaware county. could lend a hand if your close.

[falcon556]

Posted in eror

[falcon556]

most obviuos way to check for a vacuum leak is that you can hear it. other way is to trace your lines and look for crackes and spray wd40 on the lines and listen for increase in rpm.

also, when you found loose manifold bolts and tightened them, did you look for missing ones. i know on my 89 i had a few loose and was completely missing one.

oh, where are you located near philly? im in delaware county. could lend a hand if your close.

Those manifold gaskets don't last for ever.
They are cheap and easy to replace. I wonder how much difference a new gasket will make.

[joshv98xj]

When I sprayed the carb cleaner around the manifolds, I didn't notice much of an rpm change, so I think the manifolds are good. I'll have to double check the bolts when the engine is cold, lately I've been trying to work on it while it is hot. I'm in Montgomery county, just off of 276, near 611 (turns into Broad St. in the city). I'd love a hand, but right now my time is limited. I'm leaving in a week to go to upstate NY to work at a camp for the summer. I'm trying to iron out some of these idle issues before I drive it up there, but my wife and I also have to pack up and move out of our apartment, so there is a lot going on right now. I've got free time during the day on Thurs and Friday, as my last day of work was today. If any of that works for you, let me know-

[Ecomike]

Two problems I see. One you still need to clean both ends of that braided wire, the flat surfaces on the ends of the braided wire, and the flat surfaces on the block and firewall that they mate to with sandpaper or scotch brite.

Second, you missing half of the battery ground wire. The OEM wire runs from the battery to the engine (like yours) but then contunes on with the same huge wire to the fire wall. So you are missing that huge ground wire from the battery to the firewall that runs across the engine block first.

Those may be your only 2 problems! Somebody took a short cut (before you) in replacing the battery to engine to firewall main ground cable.

Lastly, as I recall there were 3 or 4 extra small ground wire connections on mine next to the dip stick beside the one huge one from the battery. Don't know where they all went as they disapear into the wiring harness bundle on mine. But there was more than just 2 more there.

[8Mud]

I read back through your post again. It sounds like what my 88 was doing. Turned out to be the TPS. When I unplugged the TPS, the idle went down. Replaced the TPS and the idle stayed down. My high idle problems started after an engine wash.
I added another ground from the battery ground to the front clip and another from the dipstick to the firewall. You really can't have too many grounds. Way not have a little redundancy.
A quick way to test the ground circuit for your TPS, is to leave the connector connected, cut a small slit in the insulation on the ground wire, TPS side of the connector. Turn the key to run and measure with a volt meter from the TPS ground to chassis ground. It's called standing voltage and tells you roughly how much resistance there is in the circuit and how much affect it is having on the voltage your trying to push. Disconnect the plug and measure the ground wire to chassis ground with an ohm meter, there will typically be a small resistance built into the circuit.
I've tested every wire from every sensor, from the sensor to the ECU or TCU and then to ground in my XJ. I've found numerous choke points.
Sometimes it's a faulty sensor, sometimes poor contact in a connector, sometimes a little of both.
I've actually found wires fatigued all the way through, under the insulation where you can't see it, at the firewall end of the injector harness. The O2 sensor harness rubbing on the exhaust manifold, pins pushed partially out of connectors, corroded connectors and corroded ground rings. Some of the ground rings aren't soldered to the wire and can corrode and cause resistance. CPS wires cooking on the exhaust manifold. I usually swap out a sensor after checking the circuit, in my experience about half the time they circuit is faulty or has enough resistance to affect sensor values anyway.
Another little trick, cut a little slit into the insulation on your TPS wires near the connector, run the wires over the top of the TB to air box rubber elbow. You have them up high where they are easy to check. I don't even bother sealing the slit up anymore, never causes me any problems. Sure makes testing easy.

[joshv98xj]

Second, you missing half of the battery ground wire. The OEM wire runs from the battery to the engine (like yours) but then contunes on with the same huge wire to the fire wall. So you are missing that huge ground wire from the battery to the firewall that runs across the engine block first.

Does anyone have a picture of what this is supposed to look like? If not, could someone snap one and post it for me? I don't have access to any that show me how it's supposed to be- all I know is that mine is incorrect.....

[Ecomike]

Does anyone have a picture of what this is supposed to look like? If not, could someone snap one and post it for me? I don't have access to any that show me how it's supposed to be- all I know is that mine is incorrect.....
Well I just went and took photos of mine and discovered I was wrong (at least about mine having a continuous very large dia. ground cable running from the battery ground, to the block and then to the firewall. Mine stops at the engine block near the dipstick and only runs from there to the battery negative post. Now I am wondering where I got the idea it ran all the way to the firewall on the passenger side. I may have seen it in a photo or diagram somewhere else. Where is 5-90 when I need him, Help?

[Ecomike]

joshv98xj,

I was wrong (as I listed below) looks like all you still need to do is clean the flat contact surfaces on both ends of the silver braided ground wire on the passenger side. It is also a critical sensor ground for the Renix controls.

[Flash]

joshv98xj,

I was wrong (as I listed below) looks like all you still need to do is clean the flat contact surfaces on both ends of the silver braided ground wire on the passenger side. It is also a critical sensor ground for the Renix controls.


I would bet that that extra wire your talking about is in 5-90 Custom ground kit!!


Flash.

[joshv98xj]

Well, I'm at a loss for what to do. I cleaned the braided wire, no change. I checked the calibration of the TPS afterwards, still at .85. I sprayed carb cleaner on the majority of my vacuum connections- didn't find anything. What are the chances that my idle is just set wrong? Should I take it to my mechanic (whom I trust completely) and let him play with it? I ran the tests of the map MAP and TPS sensors, which showed they are working. I'm really all out of ideas. :dunno: :dunno: :dunno: :dunno: :dunno:

[langer1]

No one said they checked the coolant and Air temperature sensors did they, if it don't sense a warm engine the idle will be high.

The Gage uses a different sensor.

[Ecomike]

.85 for the TPS idle setting is still too high, needs to be between .80 and .82

I think langer 1 is right, I do not see where joshv98xj has tested the two ECU temperature sensors, namely the air intake manifold temperature sensor which is toward the firewall on the top of the air intake manifold and the coolant temperature sensor hiding under the two manifolds in the drivers side of the block. I think I got confused between this thread and 2 others this week working on similar idle problems.

If the coolant sensors are OK (you need to test them cold and hot with the ohm meter while disconnected), and once the TPS is set to .82 Volts at idle (the difference between .82 and .85 volts is several hundred RPM!), and once you are convinced the grounds are good, if you still have a high idle I would bit the bullet and replace the manifold gaskets (intake and exhaust) and the throttle body gasket.

You said you cleaned the braided ground wire, but did not say you cleaned the contact on each end, and the surfaces they make contact with (sorry for being an#l, but trying to be thourough at this point.)

Use the ohm meter to test between the engine block and the battery ground, engine block and clean bare spot on the firewall, and the firewall and the battery ground all with the power turned off. They should all read less than 1 ohm. If one or more reads higher than 1 ohm you still have a ground problem. There are three temperature sensors, the one on the rear drivers side threaded into the engine head itself is just for the gauge. The other two report to the computer, ECU, they should read 3,400 ohhms at 70 F, 7,500 ohms at 40 F, 1,600 ohms at 100 F, 450 ohms at 160 F, 185 ohms at 212 F.

You can eliminate the IAC as a major issue by disconnecting it at cold start up at a lower idle. With the IAC disconnected the idle should only increase by 200 to 300 rpm as the engine warms up under normal circumstances (based on tests I ran with a working, normal system). With IAC disconnected the ECU can not adjust it, so this helps isolate the cause of the increasing idle. If it runs up by 800 rpm from say 700 to 1500 rpm as it warms up that leaves ground issues, vacuum leaks that are changing rates with temperature increase, or a bad temperature sensor in the air intake manifold ot the coolant temp sensor in the block.

[falcon556]

vacuum leaks that are changing rates with temperature increase, or a bad temperature sensor in the air intake manifold ot the coolant temp sensor in the block.

I still think that the vacuum issue which is easy to check has not been completely explored. Spraying carb cleaner tells a lot but not eveything. If the leak is further down the line, you will never find it.
I think it is time to plug at the sourse. Remove the line at the manifold and plug it.
For example a leaking reservoir cannot be detected by spraying. An internal leak at the cruise servo, motors for the heater etc.

[joshv98xj]

Question- is the TPS setting different for a manual than it is for an auto? I Chilton's doesn't differentiate, but I read another post that says it's .82 for auto, and .17 for manual?

[8Mud]

Question- is the TPS setting different for a manual than it is for an auto? I Chilton's doesn't differentiate, but I read another post that says it's .82 for auto, and .17 for manual?
The TPS is two parts for the auto, actually two TPS's sandwhiched together. The tranny half (front/outer) starts at 82% of input voltage and drops as the throttle is applied. The ECU (computer half) starts at 18% of input voltage and rises as the throttle is applied. For the Renix.
There is a little flexibility in the adjustments, a little plus and minus doesn't seem to hurt things much.
But to make things interesting the base voltage for the TCU half of the TPS originates at the TCU and the ECU half of the TPS base voltage originates at the ECU and they can sometimes be fairly different. Making it highly unlikely to ever get a true 82% 18% ratio on either and have your motor run correctly or the tranny shift properly.
Unequal grounds can also cause much the same problem. There are two ground rings on the dipstick holder. One for the TCU and one for the ECU. I've noticed more than a few XJ's, where the ground ring for the TCU, is only crimped and not soldered and fairly corroded.

[joshv98xj]

I've been following this post, trying to diagnose the idle problem on my MJ, an '88, 4.0, 5spd. Have I set the TPS wrong if I've set it to approx .82 with my multimeter? Should I instead be at around .18 since it's a 5spd?

[Ecomike]

Question- is the TPS setting different for a manual than it is for an auto? I Chilton's doesn't differentiate, but I read another post that says it's .82 for auto, and .17 for manual?
I would say the posted .17 is wrong, maybe a typo. Where is it posted?

My Renix, 87 FSM does not list a different TPS voltage setting for Manual transmissions, but since there is no second half of the TPS on manual transmission models the front half is the only part to calibrate. I have seen a variation from 0.80 to 0.82 in different year FSMs, varies over the years, for the TPS Idle setting on the front half regardless of the transmission, for 4.0 engines.

Maybe the .17 was for a different engine?

[Ecomike]

The TPS is two parts for the auto, actually two TPS's sandwhiched together. The tranny half (front/outer) starts at 82% of input voltage and drops as the throttle is applied. The ECU (computer half) starts at 18% of input voltage and rises as the throttle is applied. For the Renix.
There is a little flexibility in the adjustments, a little plus and minus doesn't seem to hurt things much.
But to make things interesting the base voltage for the TCU half of the TPS originates at the TCU and the ECU half of the TPS base voltage originates at the ECU and they can sometimes be fairly different. Making it highly unlikely to ever get a true 82% 18% ratio on either and have your motor run correctly or the tranny shift properly.
Unequal grounds can also cause much the same problem. There are two ground rings on the dipstick holder. One for the TCU and one for the ECU. I've noticed more than a few XJ's, where the ground ring for the TCU, is only crimped and not soldered and fairly corroded.

I must agree, "Very Interesting" indeed!

I wonder if a precision resistor in one side to correct the imbalance would be worth investigating?

I have always just set the ECU side and pretty much ignored the TCU side. I am starting to wonder if that was a mistake. I am still getting less mileage than I think I should (10-12 local, maybe 15 to 16 highway), and have to get my speed up to 42 to 43 mph to get the last shift (4th or clutch lock up, not sure which it is yet, I am thinking 4th). If I go from zero to 35 and cruise at 35 mph I am still at 1800 rpm, if I go to 42 mph and drop back to 35 mph cruising the RPM is at 1100 to 1200 rpm.

[8Mud]

I must agree, "Very Interesting" indeed!

I wonder if a precision resistor in one side to correct the imbalance would be worth investigating?

I have always just set the ECU side and pretty much ignored the TCU side. I am starting to wonder if that was a mistake. I am still getting less mileage than I think I should (10-12 local, maybe 15 to 16 highway), and have to get my speed up to 42 to 43 mph to get the last shift (4th or clutch lock up, not sure which it is yet, I am thinking 4th). If I go from zero to 35 and cruise at 35 mph I am still at 1800 rpm, if I go to 42 mph and drop back to 35 mph cruising the RPM is at 1100 to 1200 rpm.

When I quoted the 18% number that was fairly specific for my XJ, my input voltage for the ECU side of the TPS, is around 4.62 X .18 (18%) = .83.
But to get acceptable shifts and a decent idle. I set the ECU side at .75 volts (16.5%) and the TCU side at 3.8 volts and increased my gas mileage by 6%. My numbers are a bit plus/minus.
It has been mentioned in the past that 84% and 16% are the outside performance settings.
I just tried to set mine to shift with 30 inch tires I have (just a little late) and to idle somewhere between too high and too low (temperature dependent).
I was thinking maybe just a cross over wire between the TCU and ECU power IN wires and got a bit nervous about it. A diode loop would likely be a better solution.
My two power inputs a have a significant difference, all the units may not be the same. Renix electronics are fairly primitive. It's worth a look if you are having trouble getting the TPS dialed in though.
I got which side of TPS is which, bass ackwords, the ECU side is the three pole connector and the TCU is the four pole connector. I think I got that right anyway. :)

[Ecomike]

When I quoted the 18% number that was fairly specific for my XJ, my input voltage for the ECU side of the TPS, is around 4.62 X .18 (18%) = .83.
But to get acceptable shifts and a decent idle. I set the ECU side at .75 volts (16.5%) and the TCU side at 3.8 volts and increased my gas mileage by 6%. My numbers are a bit plus/minus.
It has been mentioned in the past that 84% and 16% are the outside performance settings.
I just tried to set mine to shift with 30 inch tires I have (just a little late) and to idle somewhere between to high and too low (temprature dependent).
I was thinking maybe just a cross over wire between the TCU and ECU power IN wires and got a bit nervous about it. A diode loop would likely be a better solution.
My two power inputs a have a significant difference, all the units may not be the same. Renix electronics are fairly primitive. It's worth a look if you are having trouble getting the TPS dialed in though.

I have to agree, tying those two power supply outputs together would be real risky!!!!!! They just might fight one another and burn themselves out in the process.

I have another option. I have been collecting working spare Renix ECUs and spare TCUs, I may just test out the different TCUs I have for volatge outputs and play with picking, matching the best one to my system. I am pretty happy with the current ECU I am using, but that could change as I do more testing.

I lucked out last year and bought a Matco MD-59 analyser on Ebay (mini laptop size, sold for about $8,000 in the late 80's) that I need to reuse and retest my Renix Engine beast with. I used it once last year, 12 months ago, and it said I essentially that I had a perfectly working new like, excellent running engine and ignition system (240,000 miles on it). It runs an osciloscope like test/program that gives you data on each cylinder and each fuel injector telling you if the injectors, cylinders, valves, spark, etc are working optimally or not. Electronically detects bad injectors, valves, bad compression, poor spark, etc. Hell of tool. Amasing the tests it can run and generate on a fuel injected engine.

[8Mud]

Question- is the TPS setting different for a manual than it is for an auto? I Chilton's doesn't differentiate, but I read another post that says it's .82 for auto, and .17 for manual?
The .82 is actually ? % of input voltage, the .17 is 17% of input voltage. If your input voltage was say 4.8 X .17 (17%) = .816 (.82 volts everybody refers to).
Clear as mud?
Don't get percents confused with voltages.
The .82 for the auto is actually 82% of input voltage and you ignore the other half of the TPS (ECU). I guess they figure the tranny adjustment is the more critical of the two.
But if the tranny adjustment, pushes the ECU half of the TPS out of the envelope, bad things can happen. There is some flexiblity built into the system. You have to figure the TPS input voltage values likely change a little anyway, as the alternator voltage changes. I doubt the IN voltage is perfectly stabilized.

[8Mud]

I have to agree, tying those two power supply outputs together would be real risky!!!!!! They just might fight one another and burn themselves out in the process.

I have another option. I have been collecting working spare Renix ECUs and spare TCUs, I may just test out the different TCUs I have for volatge outputs and play with picking, matching the best one to my system. I am pretty happy with the current ECU I am using, but that could change as I do more testing.

I lucked out last year and bought a Matco MD-59 analyser on Ebay (mini laptop size, sold for about $8,000 in the late 80's) that I need to reuse and retest my Renix Engine beast with. I used it once last year, 12 months ago, and it said I essentially that I had a perfectly working new like, excellent running engine and ignition system (240,000 miles on it). It runs an osciloscope like test/program that gives you data on each cylinder and each fuel injector telling you if the injectors, cylinders, valves, spark, etc are working optimally or not. Electronically detects bad injectors, valves, bad compression, poor spark, etc. Hell of tool. Amasing the tests it can run and generate on a fuel injected engine.
My method is the old butt dyno and simple multimeter tests. When something gets seriously out of wack, I notice pretty quick. My old XJ is a hard used 88, that I manage to barley keep up with. Though I have to say everything works, but the door locks (reliably), my headliner is slowly becoming a lap blanket and some oil seeps. Next project. I just managed to get the power windows to double there speed (last project), I'm fairly proud of that.:D

[Ecomike]

You just had to go and MUDdy up the water, LOL.:D Well some folks here love mud from what I hear.:roflmao:

Anyway, Good answer!!!!!!

I see where some confusion comes from as the .82 is also the idle voltage setting listing in one of the FSMs I have in pdf form, 89 year I think, and mine is 0.80 Volts, 87 year for the front, ECU side of the TPS. My 87 year FSM, Renix FI manual, says to set the ECU-TPS idle to 0.80 volts (apx) with the engine off and power on, which eliminates the alternator voltage regulator influence. It says nothing about the percentage values of input voltage at idle and WOT. It also says input volatge (pin A to Pin B of the front ECU connector) should be apx 5.0 volts.

It also says nothing about setting the TCU-TPS voltages or using percentages on the TPS using the square TCU to TPS connector.

But I have read here and elsewhere ( I forget where exactly) about the percentage setting procedure you and some others are using and I have read where some use the TPS-TCU connector for setting the percentage volatges.

I have just never tried it. Do you have any idea where the percentage method and the TCU-TPS settings originated????

The .82 is actually ? % of input voltage, the .17 is 17% of input voltage. If your input voltage was say 4.8 X .17 (17%) = .816 (.82 volts everybody refers to).
Clear as mud?
Don't get percents confused with voltages.
The .82 for the auto is actually 82% of input voltage and you ignore the other half of the TPS (ECU). I guess they figure the tranny adjustment is the more critical of the two.
But if the tranny adjustment, pushes the ECU half of the TPS out of the envelope, bad things can happen. There is some flexiblity built into the system. You have to figure the TPS input voltage values likely change a little anyway, as the alternator voltage changes. I doubt the IN voltage is perfectly stabilized.

[Ecomike]

Well I just collected some data on my power on, engine off,TCU-TPS square connection all at Idle:

A-B = .29 V
A-D = 4.36 V
B-D = 4.65 V

A-ground = 5.45 V
B-Ground = 5.16 V
D-ground = 0.80 V
---------------------------
Power off ohm readings:

A-Gorund = 550 ohms
B-ground = 1550 ohms
D-ground = 1355 ohms

A-B = 1025 ohms
A-D = 1074 ohms
B-D = 1963 ohms

I need an extra pair of hands or tool to run the tests at WOT. Maybe do that later. I was surprised to see all these resistance readings with the power off. I expected one to be a ground at least and one to have infinite resistance to ground.

Hmmmm?

[8Mud]

You just had to go and MUDdy up the water, LOL.:D Well some folks here love mud from what I hear.:roflmao:

It also says nothing about setting the TCU-TPS voltages or using percentages on the TPS using the square TCU to TPS connector.

But I have read here and elsewhere ( I forget where exactly) about the percentage setting procedure you and some others are using and I have read where some use the TPS-TCU connector for setting the percentage volatges.

I have just never tried it. Do you have any idea where the percentage method and the TCU-TPS settings originated????

In the FI section of the 88 FSM there is a procedure for setting the TPS. That actually confuses the heck out of me. In a perfect world with a 5.0 volt input to the TPS. the ECU side should read .8 volts M/T and TCU side 4.2 volts A/T. I'm not going to go into which pins are which.
All data recommends (I think) 82% of the input voltage for the TPS A/T. I've read both 82% and 83% in various places. And I've read both .8 and .82 volts for the M/T in various places.
I've never seen a Renix with 5.0 volt input voltage, it's usually somewhere between 4.6 and 4.8.
Sorry if I confused anybody, the more I think about it the harder it gets to understand.
Some of the confusion is trying to decide whether to set the TPS at ideal voltages designed for a 5.0 volt input or as a ratio.
.84 (84%) X 5.0 volts = 4.2..... .16 (16%) X 5.0 = 0.8.... 84% + 16% = 100% (interesting but irrelevant). The input voltage is rarely (if ever) 5.0 volts. The closer you set one side of the TPS to the ideal index voltage (of 4.2 volts for the A/T) the lower the other side gets ( away from the ideal 0.8 volts for the ECU).
Manual tranny is much easier, you only have one voltage to contend with, 0.8-.82 volts, the ideal setting.
IMO there is no ideal number in a practical sense. It's a conundrum, with no perfect definitive answer. Most people seem to agree that the TPS, TCU, A/T setting is the more critical of the two.
The start of the thread was high idle, the ECU side of the TPS being way out, can cause a higher than normal idle, as can a faulty TPS. And bad grounds, or high resistance in the wiring etc.

[8Mud]

Well I just collected some data on my power on, engine off,TCU-TPS square connection all at Idle:

A-B = .29 V
A-D = 4.36 V
B-D = 4.65 V

A-ground = 5.45 V
B-Ground = 5.16 V
D-ground = 0.80 V
---------------------------
Power off ohm readings:

A-Gorund = 550 ohms
B-ground = 1550 ohms
D-ground = 1355 ohms

A-B = 1025 ohms
A-D = 1074 ohms
B-D = 1963 ohms

I need an extra pair of hands or tool to run the tests at WOT. Maybe do that later. I was surprised to see all these resistance readings with the power off. I expected one to be a ground at least and one to have infinite resistance to ground.

Hmmmm?

I'm fairly certain you test with the key in the run position and the motor off.
The chassis to ground readings are kind of irrelevant, though some people have grounded the TPS, TCU ground circuit to chassis ground in the past.
Your A to D voltage looks a little high, late shifts?

[Ecomike]

I'm fairly certain you test with the key in the run position and the motor off.
The chassis to ground readings are kind of irrelevant, though some people have grounded the TPS, TCU ground circuit to chassis ground in the past.
Your A to D voltage looks a little high, late shifts?

I find that at this stage of the game no data is truely irrelevant. Better to have too much data as it sometimes gives a clue as to what is really going on, how to how the beast really works or what is really wrong. I posted it for possble future reference by me and others for now. Just being thourough, habit comes from doing research work.

Anyway, Yes all the published test procedures are power on, engine off, but you can not measure ground resistance and signal wires that should not be grounded but maybe have bad insulation somewhere that is partly leaking voltage to ground with the power on. That is why I took all the extra readings.

I am not sure what you mean by chassis to ground, do you mean ECU/TCU sensor ground to car body chassis ground? In mine case I am pretty sure mine is currently well under 0.5 ohms. Which is why I am surprised at all the high readings I see on the TCU/TPS side. I expected one of them to be less than 1 ohm.

[Ecomike]

Well I dug out all my old notes and print outs of how to's on this topic and Pin D is suppose to be ground, with less than 1 ohm to ground! I would say that 1550 ohms is just a little shy of that mark, yes? :shocked:

Well I did some further testing, I had the Pin A to D and Pin B to D volatges backwards. A to D 4.65 and B to D was 4.36 volts. I ran a new ground wire from the sensor harness, Pin D to the battery negative post. I have a good ground now, Pin D to ground reads about 0.7 ohms now from the sensor side of the connector and about 0.1 ohms from the other side. With the power on Pin D to ground reads 0.01 volts! Much better!

Interestingly Pin A to B still reads 0.29 V, Pin A to D still reads 4.65 V, Pin B to D still reads 4.36 V, but Pin A to ground now reads 4.67 V, Pin B to ground now reads 4.38 V and Pin D to ground reads 0.01 V.

I gave it a test drive and I think I see and feel some differences, but I have read that the TCUs go through a relearn procedure so I will take a few short trips including the highway and report back in few days as to what final differences it has made in the transmission operation. I definately noticed later shifts at WOT since adding the new ground wire to the TCU side of the TPS!:sunshine: It was still shifting too soon before this ground repair, like around 2000 rpm, it got up to nearly 3000 rpm in second this time before shifting to third at WOT.

One would think that after all the preaching I have done lately about good grounds, that I would have all good grounds on mine by now.:laugh: You Think?

[8Mud]

Well I dug out all my old notes and print outs of how to's on this topic and Pin D is suppose to be ground, with less than 1 ohm to ground! I would say that 1550 ohms is just a little shy of that mark, yes? :shocked:

Well I did some further testing, I had the Pin A to D and Pin B to D volatges backwards. A to D 4.65 and B to D was 4.36 volts. I ran a new ground wire from the sensor harness, Pin D to the battery negative post. I have a good ground now, Pin D to ground reads about 0.7 ohms now from the sensor side of the connector and about 0.1 ohms from the other side. With the power on Pin D to ground reads 0.01 volts! Much better!

Interestingly Pin A to B still reads 0.29 V, Pin A to D still reads 4.65 V, Pin B to D still reads 4.36 V, but Pin A to ground now reads 4.67 V, Pin B to ground now reads 4.38 V and Pin D to ground reads 0.01 V.

I gave it a test drive and I think I see and feel some differences, but I have read that the TCUs go through a relearn procedure so I will take a few short trips including the highway and report back in few days as to what final differences it has made in the transmission operation. I definately noticed later shifts at WOT since adding the new ground wire to the TCU side of the TPS!:sunshine: It was still shifting too soon before this ground repair, like around 2000 rpm, it got up to nearly 3000 rpm in second this time before shifting to third at WOT.

One would think that after all the preaching I have done lately about good grounds, that I would have all good grounds on mine by now.:laugh: You Think?
I've been through about everything you've been through numerous times. Trying to figure out where the choke points are in the ground circuit and where the resistance is in the power in and reference signal voltages.
There is a built in resistance in the TCU and the ECU. The ground circuit goes from the TPS back to the module and then to ground at the dipstick. The modules (both TCU and ECU) have a built in resistance in the ground circuit). I've tested four, the resistance is fairly constant in the TCU and ECU, leading me to believe it is supposed to be there. My guess would be some sort of surge protection, maybe a simple capacitor. I picture a ladder circuit with a capacitor in the ground leg, though I may be wrong.
I've been hesitant to ground the TPS ground circuit to chassis or battery negative ground. For the simple reason, the resistance in the module (ground circuit) may be a necessary part of the electronics package.
I gave up trying to identify the pin numbers long ago (bad eyes) There is only three wires black blue and gray (depending on which side of the connector your looking at). Black is ground, the other two are either the input voltage or the output voltage.

This setup makes testing and adjustment much quicker and easier, though the connectors may rub the hood insulation some. This way only takes two hands. :)
http://i9.tinypic.com/6cg5jsj.jpg

[Ecomike]

When I fixed the ground near the dip stick my ECU to TSP connector ground (ie the ECU ground) it read less than 1 ohm, most of which is from a very old tired TSP to ECU wiring harness connector (based on testing both sides of the connector). So I have never seen any internal ECU ground resistance!

I made three short trips so far, more testing planned since adding a new direct ground to the TCU-TSP ground wire.

Unless I am mistaken ( I thought I was wrong once, but it turned out I was wrong, LOL!), that TSP to TCU square connector in the photo you just posted is connected 180 degrees off, back wards, flip flopped 180 degrees. I base that on the fact that two of the wires, one on each side are not connected to anything the way it is connected in that picture! It may just be the angle of the photo, but it looks like there is no wire A on the left side???? Actually the more I look at it the connectors look to be attached correctly, but wire A on the left side looks to be in slot C?

I've been through about everything you've been through numerous times. Trying to figure out where the choke points are in the ground circuit and where the resistance is in the power in and reference signal voltages.
There is a built in resistance in the TCU and the ECU. The ground circuit goes from the TPS back to the module and then to ground at the dipstick. The modules (both TCU and ECU) have a built in resistance in the ground circuit). I've tested four, the resistance is fairly constant in the TCU and ECU, leading me to believe it is supposed to be there. My guess would be some sort of surge protection, maybe a simple capacitor. I picture a ladder circuit with a capacitor in the ground leg, though I may be wrong.
I've been hesitant to ground the TPS ground circuit to chassis or battery negative ground. For the simple reason, the resistance in the module (ground circuit) may be a necessary part of the electronics package.
I gave up trying to identify the pin numbers long ago (bad eyes) There is only three wires black blue and gray (depending on which side of the connector your looking at). Black is ground, the other two are either the input voltage or the output voltage.

This setup makes testing and adjustment much quicker and easier, though the connectors may rub the hood insulation some. This way only takes two hands. :)
http://i9.tinypic.com/6cg5jsj.jpg

[8Mud]

When I fixed the ground near the dip stick my ECU to TSP connector ground (ie the ECU ground) it read less than 1 ohm, most of which is from a very old tired TSP to ECU wiring harness connector (based on testing both sides of the connector). So I have never seen any internal ECU ground resistance!

I made three short trips so far, more testing planned since adding a new direct ground to the TCU-TSP ground wire.

Unless I am mistaken ( I thought I was wrong once, but it turned out I was wrong, LOL!), that TSP to TCU square connector in the photo you just posted is connected 180 degrees off, back wards, flip flopped 180 degrees. I base that on the fact that two of the wires, one on each side are not connected to anything the way it is connected in that picture! It may just be the angle of the photo, but it looks like there is no wire A on the left side???? Actually the more I look at it the connectors look to be attached correctly, but wire A on the left side looks to be in slot C?
Got it! Thanx for bouncing some ideas around with me.:D You were right the resistance I was testing in the ECU was in the connectors.
The major problem was the sensor circuit shared ground splice under the harness plastic sheath, maybe 8 inches on the sensor side of the C101 connector. Three sensor wires, TPS, Engine temp. to ECU ground and another I haven't idenitified. Go to one ground wire through the C101 and then to the ECU. Long story short, somebody did a poor job of crimping the squeez connector. I had between 4.5 and 61 ohms of resistance depending on how I twisted the harness.
Thanx again even the small successes make you feel good.

The TPS, TCU connector wires are OK, just in a knot on the far side of the connector.

Take your TCU out and check the resistance between the D-3 (TPS grd in) and D-7 (TCU grd out) pins. Sure acts like a condenser when I tested it. Somebody once told me a condenser was unlikely, more likely a capacitor in the ground circuit. MY XJ shifts well going up and down shifts. My schematic says the C-5 pin is also some sort of ground, but I had no success testing for a through ground, it's likely the ground leg of some sort of circuitry.
Both the TCU on my XJ and my spare test the same.

Your right there is no resistance in the TPS to ECU ground circuit, that was just in my harness. Fooled me because both the TCU and ECU ground circuit had about the same resistance */- allowing for line loss and less than perfect connections. Assumptions will bite you in the rear most every time.

[Ecomike]

Well I have been running tests on the TCU and TCU side of my TPS (my TPS is not very old) and have found some intersting values, & problems. But first here is the link to the pin outs and proper volatges for testing the Transmission Control Unit (TCU) for an AW4 TCU and the TCU side of the throttle Position Sensor (TPS).

http://www.transonline.com/transDigest/magazines/1997-10/Shift%20Pointers/index.html

There are 4 pages, be sure to read and print pages 1,3 & 4! This is one to be sure and bookmark!

Now on to the nasty discoveries I just made.

Everything checked out as normal except the following:

C10 read 0.5 to 2.0 volts with the brake OFF???? WTF??? and 11 Volts with brake applied which seems OK based on other battery voltage readings I got. Seems there is a small battery voltage drop between the battery and the dash area components, may be poor contacts along the way including the fuse box.....etc.

D1 was OK with 4.66 Volts and
D2 read OK at idle with 4.37 volts, BUT this is not .82 of 4.66 Volts (.82*4.66=3.82), so it seems high????

D2 read 3.78 volts at WOT.:eek: OMG! It should be like 0.5 volts apx! Some say it should 0.2 to 0.5 volts! I don't even have 10,000 miles on this TPS yet, and it has never been abused! I went and checked the reading at the TPS itself and sure enough it is way off on the range it should be giving me for the TCU side of the TPS. I tested it right across the sensor so it was not any wiring cross connects giving me the extra voltage. :eek: I Paid a god awful apx $75 for this two bit variable resistor thingy at Autozone less than 2 years ago!:eek: And I am begining to suspect it was bad when I bought it.:eek:

So I rechecked the ECU side of the TPS, and the ECU side of it looks better! It reads 0.80 volts at Idle and 3.24 Volts at WOT (which seems a little low to me?????) so maybe that is why it feels like I have 4 banger instead of 4.0 engine???? I need to recheck but I think my ECU input is about 4.7 volts. What should WOT of the ECU side of the TPS be?????

OK, other stuff, back to the TCU , I had <1.0 ohm at D7, and D3 grounds! This is good.

11.93 volts at D16 (a little low as my battery is about 12.5 to 12.9 Volts? but OK for now)

C-8, C-9, C11, C-14, C-15, C-16 all tested near perfect.

Note that unless otherwsie stated the readings are taken with the TCu connected to the wiring harness, but there a few tests listed where they tell you to power down the ignition and to disconnect the TCU from the harness and test from the harness connector pins directly, C-14 is an example!

Now the last big mystery is D-14. D-14 is suppose to have Battery volatge all the time! Only reason I can think for this is to keep volatile program memory alive!!!!!!:eek: Mine read 0.038 to 0.92 Volts with the power on and 0.01 Volts with power off! Definately a problem, but sure just how critical it is to fixing my problems.

Speaking of which I have had a lack of downshift (non-existant drop down on heavy acceleration), plus I still seem to be missing about 5 mpg of gas mileage which I suspect is related to these problems I have just finally located (only took 2 years of part time trouble shooting), and they may be affecting Torgue converter lock up.

I have been delayed working on this twice today already,
rain delays! Hasta

Lastly I find it quite puzzling that fixing the ground problem at the TPS (TCU side) yesterday did not leave a ground problem at the TCU itself????? Hmmm?

[langer1]

My Renix, 87 FSM does not list a different TPS voltage setting for Manual transmissions,

It should, they operate exactly in reverse. The % are also slightly different.

[langer1]

You got a bad ground or I should say the 5 volt ground. Which comes from the ECU.

[Ecomike]

You got a bad ground or I should say the 5 volt ground. Which comes from the ECU.


??????:dunno:

[Ecomike]

My Renix, 87 FSM does not list a different TPS voltage setting for Manual transmissions,

It should, they operate exactly in reverse. The % are also slightly different.

So what settings and % are you using on yours?

[8Mud]

Well I have been running tests on the TCU and TCU side of my TPS (my TPS is not very old) and have found some intersting values, & problems. But first here is the link to the pin outs and proper volatges for testing the Transmission Control Unit (TCU) for an AW4 TCU and the TCU side of the throttle Position Sensor (TPS).

http://www.transonline.com/transDigest/magazines/1997-10/Shift%20Pointers/index.html

There are 4 pages, be sure to read and print pages 1,3 & 4! This is one to be sure and bookmark!

Now on to the nasty discoveries I just made.

Everything checked out as normal except the following:

C10 read 0.5 to 2.0 volts with the brake OFF???? WTF??? and 11 Volts with brake applied which seems OK based on other battery voltage readings I got. Seems there is a small battery voltage drop between the battery and the dash area components, may be poor contacts along the way including the fuse box.....etc.

D1 was OK with 4.66 Volts and
D2 read OK at idle with 4.37 volts, BUT this is not .82 of 4.66 Volts (.82*4.66=3.82), so it seems high????

D2 read 3.78 volts at WOT.:eek: OMG! It should be like 0.5 volts apx! Some say it should 0.2 to 0.5 volts! I don't even have 10,000 miles on this TPS yet, and it has never been abused! I went and checked the reading at the TPS itself and sure enough it is way off on the range it should be giving me for the TCU side of the TPS. I tested it right across the sensor so it was not any wiring cross connects giving me the extra voltage. :eek: I Paid a god awful apx $75 for this two bit variable resistor thingy at Autozone less than 2 years ago!:eek: And I am begining to suspect it was bad when I bought it.:eek:

So I rechecked the ECU side of the TPS, and the ECU side of it looks better! It reads 0.80 volts at Idle and 3.24 Volts at WOT (which seems a little low to me?????) so maybe that is why it feels like I have 4 banger instead of 4.0 engine???? I need to recheck but I think my ECU input is about 4.7 volts. What should WOT of the ECU side of the TPS be?????

OK, other stuff, back to the TCU , I had <1.0 ohm at D7, and D3 grounds! This is good.

11.93 volts at D16 (a little low as my battery is about 12.5 to 12.9 Volts? but OK for now)

C-8, C-9, C11, C-14, C-15, C-16 all tested near perfect.

Note that unless otherwsie stated the readings are taken with the TCu connected to the wiring harness, but there a few tests listed where they tell you to power down the ignition and to disconnect the TCU from the harness and test from the harness connector pins directly, C-14 is an example!

Now the last big mystery is D-14. D-14 is suppose to have Battery volatge all the time! Only reason I can think for this is to keep volatile program memory alive!!!!!!:eek: Mine read 0.038 to 0.92 Volts with the power on and 0.01 Volts with power off! Definately a problem, but sure just how critical it is to fixing my problems.

Speaking of which I have had a lack of downshift (non-existant drop down on heavy acceleration), plus I still seem to be missing about 5 mpg of gas mileage which I suspect is related to these problems I have just finally located (only took 2 years of part time trouble shooting), and they may be affecting Torgue converter lock up.

I have been delayed working on this twice today already,
rain delays! Hasta

Lastly I find it quite puzzling that fixing the ground problem at the TPS (TCU side) yesterday did not leave a ground problem at the TCU itself????? Hmmm?

D-14 comes from a fusible link, through a connector, through a splice, to the D-14 pin (red) at the TCU. The splice splits the constant power to the ECU also. So if you have no power on the D-14, you likely also have no power to the ECU constant power B-7 (red).
The ECU half of my TPS is 7.5 volts and and 4.45 at WOT.
The TCU half of my TPS is set at 3.8 volts, I have 4.65 volts in X .82 (82%)= 3.8 volts. Though I have noticed, it has better shifts at around 4.0 volts (though this setting did cost me some gas mileage). It is .16 volts at WOT. This TPS is actually an original from 87, don't underrate junk yard parts. New isn't necessarily better, sometimes a tried and proven part is the better choice.
I tend to make one change at a time and drive it for awhile, before making anymore changes.

[Ecomike]

D-14 comes from a fusible link, through a connector, through a splice, to the D-14 pin (red) at the TCU. The splice splits the constant power to the ECU also. So if you have no power on the D-14, you likely also have no power to the ECU constant power B-7 (red).
The ECU half of my TPS is 7.5 volts and and 4.45 at WOT.
The TCU half of my TPS is set at 3.8 volts, I have 4.65 volts in X .82 (82%)= 3.8 volts. Though I have noticed, it has better shifts at around 4.0 volts (though this setting did cost me some gas mileage). It is .16 volts at WOT. This TPS is actually an original from 87, don't underrate junk yard parts. New isn't necessarily better, sometimes a tried and proven part is the better choice.
I tend to make one change at a time and drive it for awhile, before making anymore changes.
7.5 Volts!:gag: How the hell are you getting that at the ECU/TPS input? The books all says 5 volts input!??????

Checking my records I am starting to think my TPS is a junk yard part, but its been over 1 year now and my older records are not as good as I am keeping now. I started keeping meticulous records about 9 months ago so I could go back and see what I did when, and what effect it had. These beasts are just too complicated to depend on memory after a while.

Where does that fuse link start at?

I am sure my ECU is working, but if that B-7 is for maintaining ECU memory only, with the key off, like the TCU (I am guessing that line D-14 is power for the memory) that may be possible. I wonder if a prior owner decided to disable the memory on both????

Can you tell me any more about tracing those lines and the splice for B-7 and D-14 and for the fuse link location?????

I was shocking (shopping, LOL) for a TPS late yesterday, and found at least 5 different manufacturers brands with prices running all the way from $59 to $150 for two connector 87-90, auto transmission TPS, including Borg warner, Wells, Airtex, AC Delco, and Standard.

The best deal I found was $34.95 for an OEM TPS from Teamgrandwagoneer.com (I think it is www.teamcherokee.com (http://www.teamcherokee.com) that I started at).
:party:

I am still puzzled about that residual volatge shpwing up on the brake line "C10 read 0.5 to 2.0 volts with the brake OFF", which should be reading zero volts!

I am starting to wonder if I don't multiple wiring harness issues that I was previously unaware off.

[Ecomike]

I will post all the data and details later tonight when I get back. I took extensive ohm readings on three TPS sensors.....turned out the TPS that I posted data on below, yesterday, the one that was on my 87 XJ, the one that turned out to be part of my Transmission problems seems to have a pair of wires flip flopped internally in the TPS :shiver: on the TCU control side of the TPS based on the test results I got. I have swaped it out for a used one I have, that I also tested, one that based on the test results, should work a lot better for engine power and for transmission shifting. I have new one on order.

Details in about 4 hours. GTG.

[8Mud]

7.5 Volts!:gag: How the hell are you getting that at the ECU/TPS input? The books all says 5 volts input!??????

Checking my records I am starting to think my TPS is a junk yard part, but its been over 1 year now and my older records are not as good as I am keeping now. I started keeping meticulous records about 9 months ago so I could go back and see what I did when, and what effect it had. These beasts are just too complicated to depend on memory after a while.

Where does that fuse link start at?

I am sure my ECU is working, but if that B-7 is for maintaining ECU memory only, with the key off, like the TCU (I am guessing that line D-14 is power for the memory) that may be possible. I wonder if a prior owner decided to disable the memory on both????

Can you tell me any more about tracing those lines and the splice for B-7 and D-14 and for the fuse link location?????

I was shocking (shopping, LOL) for a TPS late yesterday, and found at least 5 different manufacturers brands with prices running all the way from $59 to $150 for two connector 87-90, auto transmission TPS, including Borg warner, Wells, Airtex, AC Delco, and Standard.

The best deal I found was $34.95 for an OEM TPS from Teamgrandwagoneer.com (I think it is www.teamcherokee.com (http://www.teamcherokee.com) that I started at).
:party:

I am still puzzled about that residual volatge shpwing up on the brake line "C10 read 0.5 to 2.0 volts with the brake OFF", which should be reading zero volts!

I am starting to wonder if I don't multiple wiring harness issues that I was previously unaware off.

Sorry about the decimal point :) should read 0.75 volts.
I always wondered if the ignition switch power in and the constant power in to the ECU power circuits were segregated. I was never curious enough to try and find out exactly what each powered up. The power line from the fusible link is fairly robust (the larger wire of the two power sources).
I have an extra harness in the garage, I'll look tomorrow and see if I can't locate the splice for you.
There is a 1.2 k resistor wired between the ignition power in circuit (D-16) to the TCU and the brake switch circuit. I've noticed it before, the resistor is not far from the inline fuse for the ignition power in circuit (behind the glove box). The one I noticed was on the outside of the harness tape.
The fuseable link is on the stater relay near the battery. I sure can't tell you which is which. But every time I trace one out, I name and mark it.

[8Mud]

Sorry about the decimal point :) should read 0.75 volts.
I always wondered if the ignition switch power in and the constant power in to the ECU power circuits were segregated. I was never curious enough to try and find out exactly what each powered up. The power line from the fusible link is fairly robust (the larger wire of the two power sources).
I have an extra harness in the garage, I'll look tomorrow and see if I can't locate the splice for you.
There is a 1.2 k resistor wired between the ignition power in circuit (D-16) to the TCU and the brake switch circuit. I've noticed it before, the resistor is not far from the inline fuse for the ignition power in circuit (behind the glove box). The one I noticed was on the outside of the harness tape.
The fuseable link is on the stater relay near the battery. I sure can't tell you which is which. But every time I trace one out, I name and mark it.
The path is from the battery to the starter relay, through a fusible link to red wire to the flat six pin connector (near the 3 or 4 relay block) to a splice about ten inches down the harness. The two red wires that go towards the firewall from the splice are the ECU and TCU constant power. The three red wires coming from the connector (towards the battery) are the power into the splice from the fusible link, power to the A/C relay and *the red power wire to the diagnostic plug/only middle pin* which would be a good spot to check for power.
It should be easy to follow the red wire back from the flat six pin connector to the fusible link. The flat six pin connector is labeled F E D C B A (the first six letters of the alphabet right to left) on my harness or my dyslexia is acting up again..

[Ecomike]

All of my fuses are good, and all my fuse links are good and I have power on both sides of all the fuse links. I will check the 6 pin connector next.

I discovered a few notable things about the TPS sensors. For instance, The upper and lower limits of the resitance readings are wider, broader, for the uninstalled TPS than they are for an installed TPS. Makes sense (not limited by the installed throttle plate limits), but affects test procedure development.

For instance the bad TPS I just replaced read 6660 ohms (idle) to 4280 ohms at WOT on the ECU side. Uninstalled at max range upper to lower (i.e not limited by the installed throttle plate limits) it read 7700 ohms to 3340 ohms.

On the TCU side of the bad TPS, pin A to pin B, it read 990 (idle) to 1100 (WOT) ohms from A to pin B, while one of the used spares I had read 2300 (idle) to 6610 (WOT) ohms on the TCU side from Pin A to pin B (and the second used spare was close to this so I am asuming this is what it should be).

What was really interesting is that the bad one, TCU side, read 4280 (idle) to 2150 ohms (WOT, uninstalled) from pin A to pin D, So it seems that the 2 wires going to pins B & D on the bad one I just replaced, which have the right colors on the outside when compared to the other 2 I have, must have gotten wired backwards at the factory in this TPS when it was made!:shiver:I am only now dscovering this since I have always been testing and calibrating the ECU side of my TPS, and ignoring for the most part the TCU side ot the tps.

So my conclusion is that we should be testing the pin to pin resistance of BOTH sides of the TPS before installation before we bother to install these, even new ones, and we should be testing unknown ones as an isolated part on the Jeep as well, just to verify that the TPS is properly wired and has the right upper and lower resistance ranges to have a chance at working properly before calibrating them with power on voltage settings.

There is still the issue of worn ones developing bad spots in service where the resistance jumps around, up and down, noisy operation, that cause random high idles, surging, hesitation, stumble, and other erratic engine speed behavior. That test seems to require an analog meter and a steady hand to test for noisy operation.

Here are the readings I got on the used one I just installed. Also these values were close the readings I got on the second used spare, and both were working pulls.

TCU Side:
Pin A to B: 2300 (idle) to 6610 ohms
Pin A to D: 4320 to 4320 ohms, constant
Pin B to D: 6620 (idle) to 2400 ohms

ECU side:
Pin A to B: 4360 to 4360 ohms, constant
Pin A to C: 6580 (idle) to 2200 ohms
Pin B to C: 2330 (idle) to 6550 ohms

Lastly the bad TPS I just replaced read 6510 ohms (idle) to 4230 ohms (WOT) pin A to Pin C uninstalled (7700 to 3300 installed) , while the spare I later installed read 6580 ohms (Idle) to 2200 ohms (WOT) uninstalled, so the old bad TPS only went from Idle to about 1/2 of WOT as far as volatge ranges go, to the ECU, due to the higher resitance and limited range of the bad TPS. As A result my ECU never saw more that 50% throttle aplied to gas peddle, something I could feel using MY seat of the pants dynomometer, LOL!

[mattbred]

I'm looking at buying that automatic TPS from teamcherokee.com for my manual transmission jeep. Would I be able to set the 3 prong connection to register 0.8 volts at idle and up to 4.8 volts at WOT? Or is it the other way around for autos?

[Ecomike]

I'm looking at buying that automatic TPS from teamcherokee.com for my manual transmission jeep. Would I be able to set the 3 prong connection to register 0.8 volts at idle and up to 4.8 volts at WOT? Or is it the other way around for autos?
According to langer 1 below:

langer1 My Renix, 87 FSM does not list a different TPS voltage setting for Manual transmissions,

It should, they operate exactly in reverse. The % are also slightly different.

Based on that I would say no! In fact from what he says you should be setting the idle to the high voltage setting, reverse of what I have been saying, as mine is automatic. perhaps some one else can confirm this?

If it is reversed on the Manual transmision version, then it should be possible to swap wires A and C (I think) and get an automatic TPS to work, unless the resistances are also different for the manual version!!!!:(

5-90 has a manual transmission, maybe you can get him to check his, and verify the correct voltage at idle and the resistance range???? I say this because I have run into enough backwrds stuff that was wired backwards, that I would want a second check to confirm that Langer 1's is not some kind of weird backwards factory error???? His post below is the first time I heard of the manual transmission version TPS being the reverse volatges of the automatic transmissions.

[mattbred]

I just tested my TPS I had laying around with a multimeter, pins A & C and when completley sprung (Ie less than idle, 0 volts etc etc) it gave a reading of 6.69k.

When I fully extended it, past what the TB arm would be, it was at 2.185k

Looking at your automatic TPS, they work the same? If this is correct, an automatic TPS WILL work with a manual ECU.

[8Mud]

I just tested my TPS I had laying around with a multimeter, and when completley sprung (Ie less than idle, 0 volts etc etc) it gave a reading of 6.69k.

When I fully extended it, past what the TB arm would be, it was at 2.185k

Looking at your automatic TPS, they work the same?
The TCU (half) TPS (auto) starts out at a low resistance between the Blu and Gry wire and the resistance goes up as the throttle is applied. Between the Blu and Blk wire it starts at a high resistance and goes down.
The ECU (half) TPS (auto) starts out with a high resistance between the Blu and Gry wires and the resistance drops as the throttle is applied. Between the Blu and Blk it starts with low resisitance and the resistance increases as the throttle is applied.
The halves are mirror image of each other.
I guess theoretically you could pick up another three pin connector, remove the pins from the four pin connector (I'm guessing that's what a stick has, I've never owned one) and swap the Gry and Blk wires and have an extra TPS for emergencies.
If I'm full of it,somebody please set me straight. Does the stick have a single three pin connector on a normal TPS?
My eyes are poor (old people problem) I really can't see the pin letters very well.
On the three pin connector A is gray, B is Blk and C is Blu. On the four pin connector A is grey, B is Blu and D is Blk. It's easier for me to sort out the colors than the letters.
If you look where the wires go into the auto TPS, you can see where the gray and black wires are swapped in position, between the two halves (the two TPS's sandwiched together). If you were to swap the wires back at the connector and change the connector to a stick type connector, you would in all likelihood have an extra stick type TPS, for emergencies. The resistance values may not be exact, but likely near enough.

[mattbred]

This is a STICK TPS Sensor. It has 3 prongs coming out of it, and at idle it starts at a high resistance, and at wide open throttle, it has a lower resistance.

http://xs215.xs.to/xs215/07221/TPS1.jpg



From all of these diagnoses, I fully believe an automatic TPS can be used with a Manual ECU.

[8Mud]

This is a STICK TPS Sensor. It has 3 prongs coming out of it, and at idle it starts at a high resistance, and at wide open throttle, it has a lower resistance.

http://xs215.xs.to/xs215/07221/TPS1.jpg



From all of these diagnoses, I fully believe an automatic TPS can be used with a Manual ECU.

If the connector on the stick TPS has female pins, it may. The wire colors for the auto ECU TPS harness end connector are.
ECU input, yellow with a Grn stripe to pin C/ to blue on the TPS pigtail wires.
5.0 volt supply is Lite Blue to pin A/ to gray on the TPS wires
Ground is Blk/with a Wht stripe to pin B/ to black on the TPS wires

The wire colors may actually be the same for the stick harness. The connector may be the same and/or have the same lock. I've seen way to many different kinds of connectors, even between different year Renix's not to mention a stick shift, to be sure of anything.
This would be a really good puzzle for 5-90 to sort out.

[mattbred]

http://xs215.xs.to/xs215/07221/TPS2.jpg

Middle is ground, rest are input/output. Looks like you could swap an auto right in.

[8Mud]

http://xs215.xs.to/xs215/07221/TPS2.jpg

Middle is ground, rest are input/output. Looks like you could swap an auto right in.
Looks the same to me.
Remember what I said about picking up another three pin connector at the junk yard and trying to rewire the TCU half of the connector as a spare ECU TPS if you install an auto type TPS. You can buy the pin removers for the connector, I have a set that really didn't cost much.
You can see here where the gray and black wires are switched in position as they enter the back of the TPS.
http://i16.tinypic.com/67o6e7b.jpg

[mattbred]

Heh I think I'd just stay with the 3 pin connector. If the connector wears out, I think your TPS itself would have wore out as well.

Im still not sure if the TPS is my problem tho I'll keep looking.

[Ecomike]

Heh I think I'd just stay with the 3 pin connector. If the connector wears out, I think your TPS itself would have wore out as well.

Im still not sure if the TPS is my problem tho I'll keep looking.

Don't know about the connector wearing out part, but once one side of the 2 part (Auto) TPS wears out, the other side may not be far behind, if it didn't aleady go bad!

[Ecomike]

This is a STICK TPS Sensor. It has 3 prongs coming out of it, and at idle it starts at a high resistance, and at wide open throttle, it has a lower resistance.
From all of these diagnoses, I fully believe an automatic TPS can be used with a Manual ECU.

Based on that I'd have to agree, looks like a direct swap. Now I am REALY wondering about what Langer 1 has since he says his works backwards???

[Ecomike]

Well after 2 years of !!!1 (At least it was starting to look that way) I have solved the last of the power problems in my 87 XJ, Wagoneer, 4.0. It was the TPS as described below. I seem to have full power restored. It is amasing how much a TPS can affect the power output of the engine and Tranny on an automatic 4.0. Anyway the used TPS sensor solved all the remaining problems as far as engine power and transmission shift points were concerned for me. Now its time to:party:



All of my fuses are good, and all my fuse links are good and I have power on both sides of all the fuse links. I will check the 6 pin connector next.

I discovered a few notable things about the TPS sensors. For instance, The upper and lower limits of the resitance readings are wider, broader, for the uninstalled TPS than they are for an installed TPS. Makes sense (not limited by the installed throttle plate limits), but affects test procedure development.

For instance the bad TPS I just replaced read 6660 ohms (idle) to 4280 ohms at WOT on the ECU side. Uninstalled at max range upper to lower (i.e not limited by the installed throttle plate limits) it read 7700 ohms to 3340 ohms.

On the TCU side of the bad TPS, pin A to pin B, it read 990 (idle) to 1100 (WOT) ohms from A to pin B, while one of the used spares I had read 2300 (idle) to 6610 (WOT) ohms on the TCU side from Pin A to pin B (and the second used spare was close to this so I am asuming this is what it should be).

What was really interesting is that the bad one, TCU side, read 4280 (idle) to 2150 ohms (WOT, uninstalled) from pin A to pin D, So it seems that the 2 wires going to pins B & D on the bad one I just replaced, which have the right colors on the outside when compared to the other 2 I have, must have gotten wired backwards at the factory in this TPS when it was made!:shiver:I am only now dscovering this since I have always been testing and calibrating the ECU side of my TPS, and ignoring for the most part the TCU side ot the tps.

So my conclusion is that we should be testing the pin to pin resistance of BOTH sides of the TPS before installation before we bother to install these, even new ones, and we should be testing unknown ones as an isolated part on the Jeep as well, just to verify that the TPS is properly wired and has the right upper and lower resistance ranges to have a chance at working properly before calibrating them with power on voltage settings.

There is still the issue of worn ones developing bad spots in service where the resistance jumps around, up and down, noisy operation, that cause random high idles, surging, hesitation, stumble, and other erratic engine speed behavior. That test seems to require an analog meter and a steady hand to test for noisy operation.

Here are the readings I got on the used one I just installed. Also these values were close the readings I got on the second used spare, and both were working pulls.

TCU Side:
Pin A to B: 2300 (idle) to 6610 ohms
Pin A to D: 4320 to 4320 ohms, constant
Pin B to D: 6620 (idle) to 2400 ohms

ECU side:
Pin A to B: 4360 to 4360 ohms, constant
Pin A to C: 6580 (idle) to 2200 ohms
Pin B to C: 2330 (idle) to 6550 ohms

Lastly the bad TPS I just replaced read 6510 ohms (idle) to 4230 ohms (WOT) pin A to Pin C uninstalled (7700 to 3300 installed) , while the spare I later installed read 6580 ohms (Idle) to 2200 ohms (WOT) uninstalled, so the old bad TPS only went from Idle to about 1/2 of WOT as far as volatge ranges go, to the ECU, due to the higher resitance and limited range of the bad TPS. As A result my ECU never saw more that 50% throttle aplied to gas peddle, something I could feel using MY seat of the pants dynomometer, LOL!

[Steve_Moore]

Good to hear , Mike. Mine's going to a mechanic again Monday .

[bn6339]

I have a question....has anyone ever replaced their TPS with a MOPAR unit, rather than an aftermarket, and without all other issues (ground, etc) still possessed problems? I have a 1990 XJ (4.0 auto) which sometimes experienced high idle, I planned to replace the TPS, and bought a MOPAR replacement. I then repaired some other things (intake/exhaust manifold gasket, oxy sensor, CPS, etc) and added a huge ground cable from the cylinder head to chassis....haven't experienced high idle for some time...

[Ecomike]

I have "New TPS" Test DATA for new, OEM, loose unmounted TPS sensors! party1:

This is for 87-90 Renix TPS with automatic transmission (has 2 pigtail connectors), tested on the 3 pin, ECU side only:

Loose unmounted, Brand New TPS tested on the ECU side itself, disconnected from harness is:

B to C - 2.360k ohms at Idle
A to B - 3.740k ohms at idle
A to C - 6090k ohms at Idle

Loose unmounted, Brand New TPS tested on the ECU side itself, disconnected from harness is:

B to C - 6.130k ohms at WOT
A to B - 3.740k ohms at WOT
A to C - 2.420k ohms at WOT

Do not confuse this with mounted TPS test results!

Also for the TCU side of the TPS, Loose unmounted TPS:

Pin B to D: 6060 ohms (idle) to 2340 ohms (WOT)
Pin A to D: 3770 idle to 3770 Ohms WOT.
Pin A to B: 2340 ohms (idle) to 6160 ohms (WOT)

[Ecomike]

Well pin D14 to my TCU which the manual says should be hot, 12 Volts from the battery all the time, was dead all the time on mine. I am sure it is a keep alive memory for the TCUs operating history (like TPS sensor data) memory.

I am guessing that it's being dead may severly affect gas mileage and I know it affects shifting performance as the manual describes a training period and directions to follow for that training period so that the TCU gets properly familiar with things like a new TPS sensor.

So I ran a new 12 volt battery wire to it today. But I went one step further and added a panel switch so I can turn it off and erase the TCU memory at the flip of a switch any time I want to. I plan on experimenting with it on multiple trips, and gauge gas mileage after training it differently.

Since I have everything else on this 87 working perfectly, finally (almost everything is brand new), this is a perfect oportunity to determine if this was one of the gas mileage problems I was I having (no TCU memory), or if it was just the bad TPS killing the mileage. Keep in mind I found a bad ground to the TCU, a bad TCU side of the TPS, and the missing memory power to the memory of the TCU all at the same time.

So now I want to know which one was limiting my mileage so severly ( I am expecting my 10 to 15 mpgs to increase substantially now). It may be the answer for dozens of others here who have experienced the same poor mileage when compared to others here with the same OEM Renix jeeps that have reported 20 to 25 mpgs.

[langer1]

None of my FSM's show any connection to D14

[Ecomike]

None of my FSM's show any connection to D14

I found it here:

http://www.transonline.com/transDigest/magazines/1997-10/Shift%20Pointers/index.html

This one is worth printing, bookmarking etc!!

[90Blue_XJ]

Ecomike,
So after all your preaching about grounds it turns out the majority of your problems were ground related. How is that dead 12v pin and switch to your TCU working? Did you have a chance to get any data on the TCUs response to haveing 12v again? Mileage?
Thanks for all your work on Renix engines and your posts here and elsewhere. You and 5-90 are the Renix gurus in my opinion. If you two should be absent an answer you dive in deep enough that is so far above my head as to impress me, which is difficult to do.
Keep up the good work.

[Ecomike]

Actually it was a lot more fun then just bad grounds. In the final analysis, regarding the high idle and low power problem, I had multiple gremlins on board. Other than my own stupid mistakes (like reconnecting the TPS and O2 sensors backwards to their wiring harnesses which caused a cyclic idle speed) and a IAT sensor (Intake Air Temperature) sensor that died along the way (caused Major cold start problems each morning in the winter), oh and finding out that the O2 sensor and CTS were not even connected in the early days when I bought it,......, the last nearly permanent fix to my random, high idle problem was permanently fixed when I had all, I mean ALL, Oh and did I say ALL, the ground wires fixed!!!!

Then my last problem, low power, and odd shifting speeds for the tranny, was solved with a new TPS. Took me two years to figure that one out! Also the replacment TPS solved the start up, 2 to 5 second high idle, which everyone says is normal! Mine is no longer normal, it goes straight to 750 rpm or at most 900 rpm idle right away, instead of 1500 for a few seconds before it drops to 750 rpm.

Sorry, but I have not, and will not be testing the 12 volt TCU fix I just did until I have a chance (dry weather needed) to replace my A/C expansion valve and recharge the A/C. Currently driving my very COLD A/C is working now, deisel jeep. Just too Dang hot and humid right now!!! I actually just finished installing the TCU memory (D-14 pin) power switch on the dash on it last night between bouts of rain here. I still need to check the B-7 pin on my ECU to see if it has the same problem the TCU D-14 pin had. I am guessing it will take a few weeks, and a few tanks of gas to have reliable, postable data on this, unless something unexpected suddenly happens first.

Ecomike,
So after all your preaching about grounds it turns out the majority of your problems were ground related. How is that dead 12v pin and switch to your TCU working? Did you have a chance to get any data on the TCUs response to haveing 12v again? Mileage?
Thanks for all your work on Renix engines and your posts here and elsewhere. You and 5-90 are the Renix gurus in my opinion.

Obiwan taught me well indeed. LOL. :yelclap:

Thanks for the compliment. party1:

Actually 5-90, 8mud, langer1, lawsoncl, oldman, and half a dozen others I can't think of at the moment, here helped me get up to speed early on. I originally started this thread as a way to keep myself straight as to what I had done, and tried and in what order, and with what results as well as a place for the experts to see what I already had done and tried all in one place.

After months of sorting through one of these multiple problem beasts it is too easy to forget what you tried, when and under what circumstances you tried it, etc.

Now it has turned into what I think is going to be one of the best Renix trouble shooting threads here.

Once the FSM troubleshooting guide falls short, I have always had a nack for being able to open up, figure out, and fix what I call black boxes. Runs in the family here.... Not afraid to go beyond the FSM when it runs out of good info and develop my own tests and procedures. Been doing that sort of thing for a long time, and back in the 90's I went back to college and learned how to write well and fast so I got good at documenting what I've done.......Anyway, I got so much great help here when I first I signed up, I decided to join in and do the same.

If you two should be absent an answer you dive in deep enough that is so far above my head as to impress me, which is difficult to do.
Keep up the good work.

[MountainRhino]

i wish this thread was a little more condensed. i hae a renix and i want to solve some of these tell tale problems. The only problem with that is after reading about 4 or 5 responses the words just go in one eye and out the other. i usually find that the last few posts i read didnt register in my mind. that most likley has to do with the amount of self induced smoke in my lungs.......(hehehe)
just the same, i cant pay attention long enough to make 9 pages of this make sense. till then i will just keep fixing stuff.
Tomarrow....a timing set. OOOHH!!! loads of fun huh?

[Ecomike]

For practice reading (and comprehension) you could try the AW4 FSM. As I recall it is much less boring (:rolleyes:) and only something like 125 pages short, LOL.:rolleyes:

Unfortunatly this is along thread, but I spent 2 years degremlinizing this Renix beast, so 9 pages ain't that bad. Perhaps one of these days 5-90 and I will get board and make a condensed visual trouble shooting guide for the Renix.

i wish this thread was a little more condensed. I have a renix and i want to solve some of these tell tale problems. The only problem with that is after reading about 4 or 5 responses the words just go in one eye and out the other. i usually find that the last few posts i read didnt register in my mind. that most likley has to do with the amount of self induced smoke in my lungs.......(hehehe)
just the same, i cant pay attention long enough to make 9 pages of this make sense. till then i will just keep fixing stuff.
Tomarrow....a timing set. OOOHH!!! loads of fun huh?

[1989cherokee]

I have had a low idle at start up and high idle when hot problem for over two years now! Have tryed evey tip posted on this site for renix equiped XJ's and still have the problem?

[Ecomike]

I gave it a short test drive today. It is working perfectly. Drives like at bat out of hell.

O to 60 in about 8 seconds now, quite a change from the 0 to 55 (top end) in 2 minutes that I got when I bought it two years ago.

The real test will be gas mileage now, that will take some time to get enough miles to see how that changed.


Ecomike,
So after all your preaching about grounds it turns out the majority of your problems were ground related. How is that dead 12v pin and switch to your TCU working? Did you have a chance to get any data on the TCUs response to haveing 12v again? Mileage?
Thanks for all your work on Renix engines and your posts here and elsewhere. You and 5-90 are the Renix gurus in my opinion. If you two should be absent an answer you dive in deep enough that is so far above my head as to impress me, which is difficult to do.
Keep up the good work.

[cygnus58]

zero to 60 in about 8 seconds. Ditto! Sounds like that's about best you can hope for stock with 176,000 miles?? (mine)
My zero to 60 problem was my CPS, engine and tach would cut out at about 2800 rpm consistantly.
I am happy with mine now.
Just thought I'd mention here what I had found and posted in another TPS thread.
If you leave the key on for about five minutes without engine running the ECU kills the 5 volts to the TPS and you must re-initialize to continue with adjustments....
I did see some mention of this in this thread but am repeating it as adjustment procedure requires the 5 volts to be there.

[tgoff]

OK I have a idle problem still. I have a 1986 2.5L TBI Renix ECU. The set up is different from later 2.5L Renix and the same as YJ 2.5L TBI Renis models. I have checked and replaced my CTS. My MAT and MAP sensors test to oem spec. I replaced all my vacuum lines (at least all I could find) except the stubs by the throttle body. I also tested and replaced my ISA. I tightened the manifold bolts as well. After all this my idle was still at around 1100-1200 rpm. I had after fire and dieseling problems during this whole time.

I then pulled off the throttle body to replace the little stub vacuum lines and reseal the throttle body. This brought my idle down to 800-900 rpm and solved the dieseling and after fire problems. I discovered the severe vacuum leak while putting sea foam through the PCV which was able to drip out at the stub vacuum connections at the throttle body. I was glad to see the idle be consistently below 1000 rpm and the engine runs a lot smoother and quieter.

800-900 rpm idle still seems high and after reading this thread my attention was brought to the TPS. Well it was barely out of spec and I adjusted it back in and it made no noticeable change to the idle.

What is the correct idle for the Renix 2.5L? I have a FSM and I cannot find the correct warm idle speed for the 2.5L TBI. The old carbureted 2.5L idle which I can find is 700 rpm. It seems that I have gone through everything but my idle is still high. Where have I yet to check? Any and all help with this PITA problem would be greatly appreciated. Thanks in advance.

[Ecomike]

The highest idle speed Haynes lists for the 2.5 L is 750 rpm so you are getting very close.

Have you gone through and verified all the sensor gound wires to be less than 1 ohm to the battery negative post? Also have you disconnected the battery for say 5 minutes to clear the Renix memory, and then restarted it to see if the idle drops?



OK I have a idle problem still. I have a 1986 2.5L TBI Renix ECU. The set up is different from later 2.5L Renix and the same as YJ 2.5L TBI Renis models. I have checked and replaced my CTS. My MAT and MAP sensors test to oem spec. I replaced all my vacuum lines (at least all I could find) except the stubs by the throttle body. I also tested and replaced my ISA. I tightened the manifold bolts as well. After all this my idle was still at around 1100-1200 rpm. I had after fire and dieseling problems during this whole time.

I then pulled off the throttle body to replace the little stub vacuum lines and reseal the throttle body. This brought my idle down to 800-900 rpm and solved the dieseling and after fire problems. I discovered the severe vacuum leak while putting sea foam through the PCV which was able to drip out at the stub vacuum connections at the throttle body. I was glad to see the idle be consistently below 1000 rpm and the engine runs a lot smoother and quieter.

800-900 rpm idle still seems high and after reading this thread my attention was brought to the TPS. Well it was barely out of spec and I adjusted it back in and it made no noticeable change to the idle.

What is the correct idle for the Renix 2.5L? I have a FSM and I cannot find the correct warm idle speed for the 2.5L TBI. The old carbureted 2.5L idle which I can find is 700 rpm. It seems that I have gone through everything but my idle is still high. Where have I yet to check? Any and all help with this PITA problem would be greatly appreciated. Thanks in advance.

[tgoff]

I reset the battery after the TPS adjustment and nothing changed. This weekend I am going to thoroughly clean the grounds and recheck my TPS and hopefully that will do the trick but aside from the slightly high idle it is running very nice.

I should have fixed that throttle body vacuum leak as soon as I saw it and not put it off for almost a year but time seems to be my limiting factor during the school year. I really can't wait to finish and start making some money.

[Ecomike]

We call those ROUNDTOITS.

Meaning, I will do it, when i get a round to it.

LOL

Enjoy school while it lasts, someday you will miss it. :read:



I reset the battery after the TPS adjustment and nothing changed. This weekend I am going to thoroughly clean the grounds and recheck my TPS and hopefully that will do the trick but aside from the slightly high idle it is running very nice.

I should have fixed that throttle body vacuum leak as soon as I saw it and not put it off for almost a year but time seems to be my limiting factor during the school year. I really can't wait to finish and start making some money.

[Eliminator89]

Just bought a 1990 Cherokee and guess what sort of problem its got? Go ahead, guess. I'll wait...

The info presented here is worth its weight in gold. Unfortunatly, I have no gold to hand out. Sorry.

Thank you guys for sharing.

[Ecomike]

Just bought a 1990 Cherokee and guess what sort of problem its got? Go ahead, guess. I'll wait...

The info presented here is worth its weight in gold. Unfortunatly, I have no gold to hand out. Sorry.

Thank you guys for sharing.

Thats OK, we're not proud, even scrap copper and steel is worth money these days!:wave:

[Eliminator89]

Speaking of copper, I just brought back about 100' of scrap 4/0 welding cable from some jobs in NE. Boss loved that! Wish I could have kept it for myself. Going back this week and will be bringing back some more (not as much though).

[Ecomike]

Getting sort of back on topic here, I got this beast (87, 4.0, Wagoneer, 248,000 miles) emission inspected in one of the tough Texas counties (Houston) earlier this week.

Here are the results:

High Speed: 2441 RPM
HC (ppm) was 8 and the limit was 220 to pass the test
CO % 0.04 and the pass limit was 1.2 %
CO2 % was 14.9
NOx was 0.00 ppm WOW!!!!! :eyes:
O2 % was 5.1


at 698 RPM (Idle) low speed results were:

HC (ppm) 28 with the pass limit being 220
CO % was 0.13 % with the pass limit being 1.20 %
CO2 was 14.7 %
O2 was 5.4 %
NOx once again was 0.00 PPM :eyes:

Not bad for a 20 year old jeep with 248,000 miles on it.

I also found out that since it is a 4x4 they do not run the stress dyno tests, seems the 4 x 4's are exempt for some reason, says they can not test them like they do 2 wheel drive cars.

[90xj06]

clearly they do not check the nox. lol

[Ecomike]

clearly they do not check the nox. lol

Not sure if you were joking or not. They do (did?) check the NOx.

Everthing except the engine under the hood is brand new (emissions and ECU wise, except the Renix ECU and CTS, or has less than 10,000 miles on it. The exhaust system, cat, pipe and muffler are brand new, less that 500 miles on them. New fuel injectors, MAP, O2 sensor, plugs, cap, rotor, wires, distributor, TPS, IAC, IAT, to name a few. The engine is running 20W50 dyno oil with one quart of Lucas oil additive and 87 octane Citgo gas.

Also I run a 165 F thermostat, but I had it up to 185 F running temp before I pulled into the inspection station.

[BlackNight]

EcoMike> If you are experiencing any or all of these symptoms. If the idle on your 4.0L Jeep motor is higher than 750-800 rpm or the idle is high and changes between 1000 to 1500 RPM after you first start the motor or stays at this RPM even after engine has reached normal operating temperature . Or when you first start the engine and it revs up to 2000 to 3000 RPM then drops SLOWELY to 1000 to 1500 RPM after 5 to 10 seconds. One thing that will also affect the RPM is the ambient Air temperature change and engine temperature changes in this condition. ANYWAY, HERE IS YOUR PROBLEM. FIX THIS AND PROBLEM GOES AWAY FOR A VERY LONG TIME. YOU HAVE A INTAKE MANIFOLD GASKET VACUUM LEAK! YOU CAN TRY RE-TORQUEING THE INTAKE BOLTS BUT THIS WILL NOT FIX THE LEAK ENTIRELY...TRUST ME ON THIS ONE. SEE, THE INTAKE MANIFOLDS ON THE 4.0L ENGINES ARE VERY PRONE TO WARPING AT THE NUMBER 6, 5, AND HALF OF #4-3 INTAKE RUNNERS. SO IF YOU TIGHTEN THE INTAKE BOLTS, ENGINE WILL RUN BETTER BUT NOT 100 PERCENT. YOU HAVE TO BUY A NEW OR GOOD USED INTAKE MANIFOLD OR IF YOU HAVE A VERY COMPITENT MACHINE SHOP IN YOUR NEIGHBORHOOD THEY CAN RESURFACE THE INTAKE MACHINED GASKET SURFACE AREA TO MAKE IT TRUE FLAT AGAIN. ALSO IF YOU OPT FOR A USED INTAKE MANIFOLD ALWAYS TAKE IT TO YOUR LOCAL MACHINE SHOP AND HAVE THEM CHECK FOR WARPAGE WITH A MACHINIST straight EDGE. AFTER YOU HAVE SOLVED THE WARPAGE PROPLEM THEN INSTALL A "NEW GASKET" AND RE CONNECT EVERYTING AND FIRE IT UP AND GO. (INTAKE MANIFOLD GASKET LEAK DOES NOT ALWAYS SHOW IT SELF ON THE 4.0L JEEP ENGINE WHEN YOU TEST FOR IT) SO TRUST ME WHEN I SAY WITH OUT A DOUBT THIS IS YOUR PROBLEM . I hope this helps and good luck and happy trails.

[Ecomike]

EcoMike> If you are experiencing any or all of these symptoms. If the idle on your 4.0L Jeep motor is higher than 750-800 rpm or the idle is high and changes between 1000 to 1500 RPM after you first start the motor or stays at this RPM even after engine has reached normal operating temperature . Or when you first start the engine and it revs up to 2000 to 3000 RPM then drops SLOWELY to 1000 to 1500 RPM after 5 to 10 seconds. One thing that will also affect the RPM is the ambient Air temperature change and engine temperature changes in this condition. ANYWAY, HERE IS YOUR PROBLEM. FIX THIS AND PROBLEM GOES AWAY FOR A VERY LONG TIME. YOU HAVE A INTAKE MANIFOLD GASKET VACUUM LEAK! YOU CAN TRY RE-TORQUEING THE INTAKE BOLTS BUT THIS WILL NOT FIX THE LEAK ENTIRELY...TRUST ME ON THIS ONE. SEE, THE INTAKE MANIFOLDS ON THE 4.0L ENGINES ARE VERY PRONE TO WARPING AT THE NUMBER 6, 5, AND HALF OF #4-3 INTAKE RUNNERS. SO IF YOU TIGHTEN THE INTAKE BOLTS, ENGINE WILL RUN BETTER BUT NOT 100 PERCENT. YOU HAVE TO BUY A NEW OR GOOD USED INTAKE MANIFOLD OR IF YOU HAVE A VERY COMPITENT MACHINE SHOP IN YOUR NEIGHBORHOOD THEY CAN RESURFACE THE INTAKE MACHINED GASKET SURFACE AREA TO MAKE IT TRUE FLAT AGAIN. ALSO IF YOU OPT FOR A USED INTAKE MANIFOLD ALWAYS TAKE IT TO YOUR LOCAL MACHINE SHOP AND HAVE THEM CHECK FOR WARPAGE WITH A MACHINIST straight EDGE. AFTER YOU HAVE SOLVED THE WARPAGE PROPLEM THEN INSTALL A "NEW GASKET" AND RE CONNECT EVERYTING AND FIRE IT UP AND GO. (INTAKE MANIFOLD GASKET LEAK DOES NOT ALWAYS SHOW IT SELF ON THE 4.0L JEEP ENGINE WHEN YOU TEST FOR IT) SO TRUST ME WHEN I SAY WITH OUT A DOUBT THIS IS YOUR PROBLEM . I hope this helps and good luck and happy trails.

I know this is a verrrrrry lonnnnng thread, but if you take the time to read most of it you will find that I already solved my problem, and it turned out to be combination of problems, some of which were intermitent, like a variable ground, loose ground connection near the oil dip stick, that was changing the TPS idle voltage by changing the ground quality of the TPS ground leg. I also had an IAT (Intake Air Temperature) sensor go south on me while I was solving the grounding problem. I also had minor CCV tubing and Valve cover gasket (vacuum) leaks that added to the diagnosis problem, and an IAC that died just about the same time the IAT sensor died.

Right now she purrrs like a kitten right nice and steady at 750 rpm in park at idle and 650 rpm in drive at idle, and she takes off like a scalled dog when you punch the gas, which is amasing since the odometer reads 248,000 miles and counting. Anthanks for the post, I am sure others will find your sugestion helpful. Just keep in mind that a vacuum leak at the intake manifold tends to cause a more steady, high idle. I had unpredictable idles running all the way from 250 rpm to 2500 rpm. The symptoms would change randomly after hours, days and weeks. Drove me nuts for almost 2 years finding and fixing all the little issues. Luckily, it was more like an occasional weekend hobby, and not a full time job figuring it out and fixing it.;)

[Ecomike]

Well the test results are in. The New TPS, Trottle Position Sensor, solved most of my low MPG problem and my low power, low torque problem.

It is the 87 renix 4.0, AW4 automatic, 4X4 Wagoneer. My old TPS tested good on the ECU side, but lacked the proper span on the TCU side. Both sides tested good at idle! The TCU side tested bad at WOT, not enough span. For more details see the old thread titled "RenX Files" (or ReniX Files?).

Anyway my old 8 mpg local, 12 to 13 mpg highway gas mileage for the last 2 years, recently tested as high as 17.7 mpg, 119.8 miles, 6.77 gallons of 87 octane gas, with 10% 0-35 mph local travel, 20% 0-45 mph semi local travel, and 70% 55 - 65 mph highway travel all in the city. Other tests got 15.4 MPG mixed city stop and go with 70% city freeway travel, some in heavy traffic, and 14.68 mpg in 232.6 miles, 15.85 gallons of mixed city with some heavy stop and go traffic on the freeways at rush hour. Based on the test results I must be near 20 mpg for pure non stop 65 mph freeway runs.

The best I got before replacing the TPS was about 13.5 mpg on a single long highway run and about 12 mpg average city. So I got a good 4 to 6 mpg increase out of the new TPS only!

The reason for the huge difference is the way the TPS signal handles the transmission operation via the TCU. The bad TPS was causing the Tranny to shift too early at too low of an engine RPM, and I believe it was reducing the tranny fluid pump pressure to the torque converter thus reducing the power transfer to the rear end from the engine.

Oh, and my old idle problems, high, low and variable, are all still gone.

249,000 miles and counting! Long live the Renix XJ!

[Slo-Sho]

just out of curiousity can you post your ecu idle, wot voltages and the tcu, idle, and wot voltages?

[Ecomike]

just out of curiousity can you post your ecu idle, wot voltages and the tcu, idle, and wot voltages?

Its already way down below in this thread, :eek: , see post number 119 in this thread, and some older test data on the bad TPS is lower down in the thread here too, like post number 116?

[Slo-Sho]

Those are OHMS, which on a pot meter can vary quite a bit. Can you post the ecu voltages at idle, wot and tcu voltages at idle and wot?

[Ecomike]

Post 98 has the voltages for a good TPS, but the 7.5 V is a typo for the ECU idle voltage, should read 0.75 V.

I deliberately went to direct resistance measurements of the mounted, and unmounted TPS with out the wiring harness conected to elliminate outside wire and ECU/TCU influences, in other words to isolate the TPS and determine what it should read by itself in ohms. If you have a good meter and a good battery in the meter the ohms readings should vary less than 1-2% between good meters, or should be accurate to within 2 significant figures if the measurement is taken in the middle of the scale (use the proper scale or range if it is not automatic), which is plenty for what we are testing. It also eliminates the variations in wiring and terminal connection resistance between vehicles and variations in the ECU output voltages.

Keep in mind those volatges you asked for will vary considerably based on the ECU and TCU output voltage and system grounds (or resistance to ground).

[Slo-Sho]

I know this, I too also have a renix and that is why I wanted to know what the voltages were in YOUR rig. Never mind then.

[Ecomike]

I know this, I too also have a renix and that is why I wanted to know what the voltages were in YOUR rig. Never mind then.

My mistake, it was post 99 I was reading and those are Mud8's numbers, not mine. Don't have time to pull those readings, got two head jobs for my kids wheels waiting on me, but I will pull them and post them when I get caught up over the holidays. In the mean time, from memory the engine off, power on TPS values were finally Text book, with 4.85 volts input at the TPS from the ECU/TCUs. I do know I had .82 V at idle on the ECU side. I finally get your point, we need to test the entire system as a last measure to see where it ended up as a system. I know I ran the tests, and as I recall they were so text book, right on that I did not record or post them. Good point

[Ecomike]

Thought I would add this to my favorite thread:

Well I confirmed my highway only mileage today on a city freeway, with frequent overpasses, not a straight flat road so it should be even better on a straight flat road, but there was no traffic so I was able to drive 48.2 miles, 99% freeway at an average of 60 mph, with a 55 mph min, 65 mph max speeds.

I topped of the tank first, until it spilled over, and topped it back off three times at the same pump, same station after the freeway trip. If I use the first gas shut off value I got it calculates to 26.34 mpgs, if I use the second pump shut off value I got, it calculates as 20.51 mpg, and the third pump shut off value which overflowed again calcualted at 18.54 mpg.

1st = 1,83 gallons
2nd = 2.35 gallons
3rd = 2.6 gallons (overflowed before shut off)

If I estimate the full tank at 2.45 gallons, just before it overflowed, I get 48.3 / 2.45 = 19.67 mpg, then times 1.02 for the tire size speedometer error, I get = 20.07 MPG!!!party1:

So I have officially joined the 20 mpg freeway/highway mileage XJ club!!!party1: :yelclap:

I am still only averaging 14 mpg due to the traffic and stop sign congestion in the local city DD routine, but even that beats what I was getting.

[Ecomike]

OK, I rechecked everthing this time on my O2 sensor, this data is correct, some of the prior data I posted may be off.

Power and engine off. Sensor disconnected. All readings were taken with the meter ground wire at the battery negative post. Cold O2 Sensor read:

Infinite resistance to ground on all three wires!!!!
__________________________________
O2 harness connection wires read:

#1 (black) 1.3 ohms
#2 (black) 4,000 ohms
#3 (orange) 53.5 ohms!!!!!!
_________________________________________
Then with all three wires connected to the O2 sensor they read:

#1 (black) 1.3 ohms
#2 (black) 4,000 ohms
#3 (orange) 8.3 ohms!!!!!!!!!
___________________________________________
Power on, engine off, all three wires connected to the O2 sensor read:

#1 (black) 150 MV ( I may need to clean and tighten my gounds again)
#2 (black) 5.00 V
#3 (orange) 11.87 V
___________________________________
Engine on, and hot:

Running 2500 rpm, then rapid decel to idle stop, I got under 1 volt for about 8 seconds after a brief rise to 3 to 4 volts for a split second!!!!!

So if renix is shutting off the fuel and running it lean the Renix FSM is wrong and the Bosch web site is right about the low voltage being lean. If the renix FSM is wrong (or mine is acting up) and the fuel is staying on during decel to 1200 rpm, then the Renix FSM is right and low volts is rich.

I got 1.5 to 4.0 volts at idle, about 1 second between swings across the 2.45 volt sweet spot at idle. Idle rpm seemed to be a bit higher (like 25 rpm higher) at 4 volts and lower at 1.5 volts!!!!

Got a rapid 2.5 to 3.5 volt swing across the 2.45 volt setpoint at 1600 to 2500 rpm steady engine speed, about 2 swings side to side per second. It finally got to a tight 3 volts at 2,400 rpm steady engine speed once the engine was good and hot (took about 10 minutes of run time). Last time I ran this test I was getting 2.45 volts almost dead on, +/- 0.1 volts, this time it was reading closer to 3 volts. :huh:

The voltage readings were taken with a high quality high impedence FET analog meter that was zeroed before the ohm tests were started. The ohms readings were taken with a high quality, high impedence digital ohm meter.

[OverTheHillsATTW]

This whole thread should be a sticky for Renix users. I went a year or two without knowing how to solve my idle problems. Here it is. If people see this they get frustrated knowing that there are more than 10 pages to view. Really its the most helpfull topic tool for Renix era engine owners and would stop alot of idle questions.

[OverTheHillsATTW]

I'm having a problem and am calling all Renix owners. I swapped TB's with my 90 renix. My shift pattern went back to normal. I took my Jeep to a friends garage to help me read and adjust anything that needed it because I still had highs and lows for an idle. We plugged in a scanner and got nothing for the throttle %. The tps isn't showing any voltage. I cleaned all my ground connections prior to this also. He printed out some computer diagrams and such and said that It seems C7 off the computer isn't sending any power to the TPS. Should I be swapping my computer also? My jeep is riding like a dog only maxing out at around 2,500 rpms and shifting no matter what. I can't get a reading out of the tps.

[Ecomike]

I'm having a problem and am calling all Renix owners. I swapped TB's with my 90 renix. My shift pattern went back to normal. I took my Jeep to a friends garage to help me read and adjust anything that needed it because I still had highs and lows for an idle. We plugged in a scanner and got nothing for the throttle %. The tps isn't showing any voltage. I cleaned all my ground connections prior to this also. He printed out some computer diagrams and such and said that It seems C7 off the computer isn't sending any power to the TPS. Should I be swapping my computer also? My jeep is riding like a dog only maxing out at around 2,500 rpms and shifting no matter what. I can't get a reading out of the tps.

Most scanners can not read the 87-90 ECU electronics. What scanner was he using? Is it actually set up for Renix? It could have been reading a problem at the scanner connector itself that is not really there in the rest of the renix circuit.

Best thing to do is get a volt-ohm meter and go take live readings right at the TPS. You might try disconnecting the battery for 30 minutes to clear the old TPS settings from the ECU memory. Once you do solve the problem with a wire patch wiring replacement, TPS calibration, and or a new TPS the renix will still act odd, idle wise for about 3 restarts till it learns the new TPS idle voltages. Most problems are caused by worn TPS internals, solved by replacing the the TPS followed by TPS calibration, and or ground wire clean up and replacements, folowed by TPS recalibration, or frequently all of the above.

[OverTheHillsATTW]

I told him about the scanner. I'm not sure what he was using but did infact have some sort of "old" jeep connector. It plugged right into my fuse relay box under the hood. I plugged my old TPS in and used my volt meter and pulled a reading of 5. I think im on the right track now. I'll have to wait a day to see how it rides. The idle went down from 2k to 1k. I just hope im not stalling out in drive. Right now im on jack stands redoing brake lines and such.

[Bent]

Not sure where to put this link but this seemed like a good spot.

Renix sensor diagnostics. (http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm)

[letank]

SNIP

I've never seen a Renix with 5.0 volt input voltage, it's usually somewhere between 4.6 and 4.8.

SNIP

The input voltage is rarely (if ever) 5.0 volts. The closer you set one side of the TPS to the ideal index voltage (of 4.2 volts for the A/T) the lower the other side gets ( away from the ideal 0.8 volts for the ECU).
Manual tranny is much easier, you only have one voltage to contend with, 0.8-.82 volts, the ideal setting.
Reviving the eternal High idle, 1990 w 2.5L 193Kmiles and 5 speed (AX5)

started to Idle high 1100-1500 but comes dow slowly to 900-1000.

Unplugged the TPS, no changes, the IAC is fully retracted.

Tested w ignition ON, engine off
CB (input-ground) 5.14V
AB (output-ground) 0.27V

Funny, everyone has too much feedback, and I am stuck w not enough.

Should I adjust to 0.8 volts or lower to 0.22 or... I am using Chryco diagnostics for 2.5 89 and 90 XJ.

How do you disco the ECU cable, I can only see one screw facing the driver

Michel
90 wranwran 2.5
74 wagoneer 5.9

[Ecomike]

Reviving the eternal High idle, 1990 w 2.5L 193Kmiles and 5 speed (AX5)

started to Idle high 1100-1500 but comes dow slowly to 900-1000.

Unplugged the TPS, no changes, the IAC is fully retracted.

Tested w ignition ON, engine off
CB (input-ground) 5.14V
AB (output-ground) 0.27V

Funny, everyone has too much feedback, and I am stuck w not enough.

Should I adjust to 0.8 volts or lower to 0.22 or... I am using Chryco diagnostics for 2.5 89 and 90 XJ.

How do you disco the ECU cable, I can only see one screw facing the driver

Michel
90 wranwran 2.5
74 wagoneer 5.9

0.83 volts is optimal for the TPS idle setting according to the last '90 FSM. Older FSM has 0.80 and 0.82 depending on year.

[letank]

0.83 volts is optimal for the TPS idle setting according to the last '90 FSM. Older FSM has 0.80 and 0.82 depending on year.

Thanks Mike, I'll play w it manana.

BTW ground tested according to specs < 1ohm, I have .5 and .3 ohm. Reading low values is always a challenge.

The diagnostic procedure (Chrysler Powertrain diagnostic procedures) that i have does not list any specific voltage, if it is below 1 volt, then test ground resistance from B terminal of TPS to vehicle ground to be less than 5 ohms, then adjust voltage to attain idle speed.

The few other thinks that i gather from web searches:
PCV, EGR, the usual vacuum leak at intake, and brake booster grommet

Michel
90 wranwran 2.5, AX15 193Kmiles
74 wagoneer 340Kmiles

[slowjeep]

my 90 4.0 is hard at startup when cold and extremely hard when warm, if I manage to start it when warm as soon as I go to gear rpms fall to 0!!!!, what 's going on?!?!?!?!?!

[88 Wagonman]

my 90 4.0 is hard at startup when cold and extremely hard when warm, if I manage to start it when warm as soon as I go to gear rpms fall to 0!!!!, what 's going on?!?!?!?!?!
Try giving it a little throttle when starting and see if it helps, if it does then go back to the begining of this thread and start reading.

[Ecomike]

Thanks Mike, I'll play w it manana.

BTW ground tested according to specs < 1ohm, I have .5 and .3 ohm. Reading low values is always a challenge.

The diagnostic procedure (Chrysler Powertrain diagnostic procedures) that i have does not list any specific voltage, if it is below 1 volt, then test ground resistance from B terminal of TPS to vehicle ground to be less than 5 ohms, then adjust voltage to attain idle speed.

The few other thinks that i gather from web searches:
PCV, EGR, the usual vacuum leak at intake, and brake booster grommet

Michel
90 wranwran 2.5, AX15 193Kmiles
74 wagoneer 340Kmiles

IIRC the 2.5 L engine has a different idle control scheem than the 4.0! Different parts, no IAC, more like an old style throttle plate external valve?

[letank]

IIRC the 2.5 L engine has a different idle control scheem than the 4.0! Different parts, no IAC, more like an old style throttle plate external valve?

Correct, it is called Idle Speed Actuator (ISA), there is no side port.

I found another link which states that the TPS voltage should be 0.2 for M/T, and throttle plate closed, BUT (yes big but) 4.6 to 4.7 volts for the M/T with the throtttle plate should wide open WOT. I have 0.23volts, did not measue the WOT value. Too much to do at this time. I am back north, jeep is south.

I am probably chasing something.... the idle speed will gradually come down. I need to digest what i found. Apparently the PS circuit has a pressure sensor that will kick the idle up while the PS pressure is high. At least i do not have A/C which has also a feedback. The ISA is also a partner responding for all the feedback.

At least i found out that the thermostat was busted.... very weak spring, the temp never went over 155F (use an infrared thermometer). I put a 180F,which allow me to calibrate the temp gauge, outside temp is in the 90ish. Let the kid drive it around town for a while, and will put a 195 later.

Michel
90 YJ 2.5l M/T 193Kmiles
74 wagoneer 340Kmiles

[letank]

my 90 4.0 is hard at startup when cold and extremely hard when warm, if I manage to start it when warm as soon as I go to gear rpms fall to 0!!!!, what 's going on?!?!?!?!?!

Stick, auto trany? How many miles.

Could be many thinks. We are more on the high idle issue. But hard starting can be so many things. We can start w the easy/inexpensive work: the fact that it is harder to start when hot is the same: weak spark is weaker when electronics heat up, weak battery, not enough juice to power relays/solenoid, corroded battery terminal or inner cable.

Check your grounds, clean up all your connectors is they are covered w oil. Time to get familiar w using a good voltmeter.

Michel
90 YJ 2.5l M/T 193Kmiles
74 wagoneer 340Kmiles

[slowjeep]

90 XJ 4.0 4wd auto 207k

[letank]

90 XJ 4.0 4wd auto 207k

Yep, I would check what i mentioned above and may be,do a compression check, or better a leak down test to see how good your engine is....

Michel
90 YJ 193K
74 wag 340K

[XJPioneer88]

I may be reviving a slightly dead thread, but this one is so darn helpful I have a 88' Pioneer 5 speed 4.0, was having this high idle problem since I bought it (About 3 months) and I found this beast of a thread.

I checked my TPS, and sure enough, there was a big hunk of carbon or something on the electrode. Picked it off, plugged it back in, haven't have a crazy, wide open 3k throttle for 4 days.

On top of that, it idles a hell of alot better, like closer to 1k rpm instead of 650 or even lower, like the thing is getting ready to kick out.

So, just wanted to say thanks for this thread.

[mntllycrzy]

so it's taken me two days of reading this thread and fartin around with the heep. I've checked, cleaned, and tightened the ground on the block, and on the firewall. I have set my tps at .83v. i have checked and replaced vaccum lines, i have checked and tightened manifold bolts. the throttle body was removed and cleaned, and the problem still persists. when i start it up, the heep idles perfect right around 700-750. once i start driving the idle sticks up at 1500-2000 rpm. this actually all started when the throttle body was removed and cleaned and reinstalled. so at this point i'm pulling my hair out and i'm stressed out over it so any help would be great. I'm pretty sure that for some reason the iac is not closing. the iac was removed, cleaned, and reinstalled. i even tried swapping it out with another jeep. i tried disconnecting the battery and leaving it disconnected. when i take the air tube off of the throttle body and the engine is running, if i put my thumb over the hole that the iac sucks air thru it idles down to about normal. so i'm pretty sure something is telling it to stay open. any thoughts?
by the way, this is an 88 4.0 with m/t. it's a 4dr laredo.
thanks in advance

[Ecomike]

You must have an intake manifold or vacuum line leak somewhere that you have missed.

When the IAC air inlet on the top of the throttle body is covered & blocked, the engine should die if there are no vacuum leaks!

How is your CCV vacuum system set up? Does it have the 2.2 to 2.8 mm orifice in the back connection line at the rear valve cover entry.

[mntllycrzy]

i don't know what ccv it has. what is ccv? all i know is that it started acting up after i cleaned the t/b

[Ecomike]

i don't know what ccv it has. what is ccv? all i know is that it started acting up after i cleaned the t/b


Crank Case Ventilation, CCV, the controlling element is an orifice about 2.5 mm inside diameter that restricts the crankcase air flow rate to the intake manifold. If it is gone and if a 1/4 ID hose or larger has been used on the back side of the valve cover connection to the intake manifold the engine gets to much air idle, and IAC becomes ineffective.
Did you use a new throttle body to intake manifold gasket?
Could some trash be stuck in the IAC port, holding the valve open?

I have occasional high idles when my floor mat gets stuck, shoved up under the gas peddle!
Be sure and check the linkage and butterfly to see if it is closing al the way!

[mntllycrzy]

butterfly is closing, nothing in iac port. i had the iac out to check. i didn't change anything in regard to hose size or anything. the lines on the tb were good. all i did was take the tb off, clean it, and reinstall it. cant be the linkage, the butterfly is shut when the idle is way up. why would the engine die when i plug the iac port? there is another hole in the tb where the engine can get air. it also has an adjuster in it.

[Ecomike]

butterfly is closing, nothing in iac port. i had the iac out to check. i didn't change anything in regard to hose size or anything. the lines on the tb were good. all i did was take the tb off, clean it, and reinstall it. cant be the linkage, the butterfly is shut when the idle is way up. why would the engine die when i plug the iac port? there is another hole in the tb where the engine can get air. it also has an adjuster in it.

Not sure about another air supply route other the IAC for idle air supply. Where is the second path you are seeing?

All the ones I have worked on that worked properly will die if you seal off the IAC air supply on the top of the TB. The only other path I know of is the CCV line with a 2.2 mm orifice, and that air is under some vacuum already and is not enough to keep the engine at idle.

[mntllycrzy]

i'm holding the tb in my had as i'm typing this. if the big spring is in the 12 position, the other orifice is in the 3 position. i'm going to get another new tb gasket tomorrow and try it again, it's just driving me nuts at this point

[8Mud]

The other port you are looking at is likely the fine adjustment for the idle (factory set, emission thing, likely minimum idle). There is a metal plug/cover that you can pry off and see the torx end of an air bypass adjustment screw. The adjustment screw is most often all the way closed from the factory. If the IAC is working properly this adjustment does very little.
You can try blowing through the orifice, though it's likely screwed all the way in from the factory or plugged with junk.
Plug off all the vacuum lines to the intake manifold, use short pieces of tubing with a screw in the end. The only vacuum line you actually need to keep the XJ running is the MAP.
If this doesn't cure your problem, I'd look at solvent or water in the TPS. The TB gasket or the intake gasket for vacuum leaks.
The TB seats itself into the gasket, if you reuse the old TB gasket you have to be careful that it seats into the indentations pressed into the gasket.

[mntllycrzy]

ive got two tb's and no metal cap on either. it doesnt idle high at first, it's totally normal until i drive it then it sticks high

[mntllycrzy]

here's another question.... this truck is a 5spd. there is a trans fuse in the fuse block. what is this fuse for? the fuse is blown and when i replaced it it blew again. what does this do and where do the wires go so i can try to trace down the short?

[Ecomike]

here's another question.... this truck is a 5spd. there is a trans fuse in the fuse block. what is this fuse for? the fuse is blown and when i replaced it it blew again. what does this do and where do the wires go so i can try to trace down the short?

It may have been an automatic, later converted to a 5 speed.

[mntllycrzy]

i kind of doubt it was converted, it was bone stock when i got it, and the one owner before me didn't say anything about changing it over. either way, where do the wires go from the fuse block?

[89xj]

i have an 89 5-speed and it also has a trans fuse. im not sure, but i think its for the back up lights. check the back up light switch on the tranny or if your back up lights are working.

as for the high idle, mine will idle to around 1100rpms somtimes when its warmed up, but not always. sometimes at a stop light when its idling high, i put it in first gear with the clutch in and with my other foot on the brake and slowly release the clutch until it slightly grabs and the idle will drop to 750 and push the clutch back down.

[mntllycrzy]

the back up switch in the trans is not plugged in so i know the lights do not currently work. I am wondering why this fuse is blown and opens as soon as a new one is installed

[mntllycrzy]

does anyone have a wiring schematic for this circuit???

[KonstantinXJ]

IAS drivers to Renix ECU is TDA2004

http://www.alldatasheet.com/datasheet-pdf/pdf/25037/STMICROELECTRONICS/TDA2004.html

:scottm:

Konstantin Grijznov.

[mntllycrzy]

i'm sorry, i don't understand how that was supposed to help

[B.RAIDER]

OPPS............Posted in wrong thread..............

[mntllycrzy]

is the tps supposed to be set at .83 or .2? is it the same for auto and manual?

[Ecomike]

is the tps supposed to be set at .83 or .2? is it the same for auto and manual?

The ECU side of the TPS (manual or automatic), (87-90 years) should read 0.83 V at idle, ignition switch power on, engine off.

[mntllycrzy]

The ECU side of the TPS (manual or automatic), (87-90 years) should read 0.83 V at idle, ignition switch power on, engine off.


so it is the same for manual and automatic? and i still check between B and C?

[Ecomike]

so it is the same for manual and automatic? and i still check between B and C?

Yes.

[mntllycrzy]

so now that i'm totally stumped do i take it to a dealer?

[Ecomike]

so now that i'm totally stumped do i take it to a dealer?

PM with the whole story, all the details, start to finish, year.....etc.

[mntllycrzy]

all the details are in the previous postings

[89xj]

so now that i'm totally stumped do i take it to a dealer?

did you get the tps wet when you cleaned the throttle body?

have you tried a new tps?

[mntllycrzy]

i didn't get it wet, i took it off the throttle body when i cleaned it. didn't use any water just gum cutter. i reset it to .83. now it idles really low at start up and it idles up higher the hotter it gets

[mntllycrzy]

i also tried a known good tps from another jeep, same effect

[mntllycrzy]

i also cleaned the air filter, i can't imagine that had anything to do with it

[89xj]

so it's taken me two days of reading this thread and fartin around with the heep. I've checked, cleaned, and tightened the ground on the block, and on the firewall. I have set my tps at .83v. i have checked and replaced vaccum lines, i have checked and tightened manifold bolts. the throttle body was removed and cleaned, and the problem still persists. when i start it up, the heep idles perfect right around 700-750. once i start driving the idle sticks up at 1500-2000 rpm. this actually all started when the throttle body was removed and cleaned and reinstalled. so at this point i'm pulling my hair out and i'm stressed out over it so any help would be great. I'm pretty sure that for some reason the iac is not closing. the iac was removed, cleaned, and reinstalled. i even tried swapping it out with another jeep. i tried disconnecting the battery and leaving it disconnected. when i take the air tube off of the throttle body and the engine is running, if i put my thumb over the hole that the iac sucks air thru it idles down to about normal. so i'm pretty sure something is telling it to stay open. any thoughts?
by the way, this is an 88 4.0 with m/t. it's a 4dr laredo.
thanks in advance

if this all started from removing the TB than recheck all your work. throttle linkage, TB gasket leak....

ive heard of people putting the arm of the TPS on the wrong side if the throttle linkage.

here is a shot in the dark that i have done on my 89. i put the vacuum line that goes to the bottom of map on the screw post of the map and not on the vacuum port. also check that the map vacuum line to the side of the TB is on the correct port. IIRC, the port on the side of the TB is a rubber piece that appears to have 2 holes when there is only one that the line can fit into.

your problem has to be the result of pulling off the TB to clean it.

[mntllycrzy]

i've had the tb off three or four times since the initial cleaning. i have replaced the new tb gasket with another new tb gasket. the vac port on the side of the tb is plugged in, i didn't remove it from the map sensor so it shouldn't be wrong. the only throttle linkage i disconnected was at the arm on the tb itself and there's only one way for it to go on. the problem definitely increases with temp i'm thinking. on cold start up it barely runs, then once it is warm it idles up to 2k. if i try another tps, one from an automatic, what happens if i plug in both connectors?

[Ecomike]

i've had the tb off three or four times since the initial cleaning. i have replaced the new tb gasket with another new tb gasket. the vac port on the side of the tb is plugged in, i didn't remove it from the map sensor so it shouldn't be wrong. the only throttle linkage i disconnected was at the arm on the tb itself and there's only one way for it to go on. the problem definitely increases with temp i'm thinking. on cold start up it barely runs, then once it is warm it idles up to 2k. if i try another tps, one from an automatic, what happens if i plug in both connectors?

Sounds like an intake manifold or exhaust manifold leak that increases in size and air flow rate as the engine warms up.

Disconnect the O2 sensor, and see if it stops. If it does stop it is the exhaust manifold leaking at the gasket or a crack in the manifold.

Check for loose manifold bolts, top and bottom.

[mntllycrzy]

i have an automatic tps, do i plug in both sensors?

[Ecomike]

i have an automatic tps, do i plug in both sensors?

You only need the flat 3 pin connector to be connected. The square 4 pin connector is for a TCU, Transmission (automatic) computer which you do not have or need since yours is a 5 speed manual transmission.

[mntllycrzy]

ok so i checked the manifold bolts. all are tight. i unplugged the 02 sensor, same problem. my xj has the extra plug for the second connector so i didn't know if i should plug it in. i plugged in the flat 3 wire job. i understand what the other connector is for. so basically i'm still in the same place. i had a perfectly normal, good running truck, then i cleaned the tb and it is going crazy

[Ecomike]

ok so i checked the manifold bolts. all are tight. i unplugged the 02 sensor, same problem. my xj has the extra plug for the second connector so i didn't know if i should plug it in. i plugged in the flat 3 wire job. i understand what the other connector is for. so basically i'm still in the same place. i had a perfectly normal, good running truck, then i cleaned the tb and it is going crazy


I have heard this story before, it was solved by replacing the throttle body with one from a junk yard. Cause was never really found, just some phantom gremlin hidden in the throttle body.

Could still be an intake manifold gasket leak.

Mine is running high again this week due to a bad brake Vacuum booster. :rattle:

[mntllycrzy]

i'm really starting to hate this truck. i don't have time to get to a junkyard and it ran perfect before hand. it's embarassing sitting at red lights with this thing runnin at 2k rpms

[mntllycrzy]

ok so here's a new development in the high idle issue. yesterday my daughters and i were driving down the highway. it was pretty warm here and they were complaining about it being hot in the heep. so when we came to the next redlight the idle was around 1800. i turned on my a/c and rolled up the windows and noticed that my idle was down to around 800. so i decided to test this. i turned the ac on and off several times while at a stop and the idle went up and down with the ac like something was telling it to go up or down. then this morning i stopped to get coffee on my way to work and it was idling high again when i stopped. i flipped the ac on just to see if it would come down and nothing, the idle stayed high.

[Ecomike]

ok so here's a new development in the high idle issue. yesterday my daughters and i were driving down the highway. it was pretty warm here and they were complaining about it being hot in the heep. so when we came to the next redlight the idle was around 1800. i turned on my a/c and rolled up the windows and noticed that my idle was down to around 800. so i decided to test this. i turned the ac on and off several times while at a stop and the idle went up and down with the ac like something was telling it to go up or down. then this morning i stopped to get coffee on my way to work and it was idling high again when i stopped. i flipped the ac on just to see if it would come down and nothing, the idle stayed high.

That sounds like a ground, ground wire problem. Have you tested the back voltage on the ground wire at the TPS on the ECU side, engine running, between that ground wire and the battery negative post? Also check the ECU grounds at the ECU.

Loose connections, moisture, heat and vibration can make the ground quality change which the ECU sees as a high TPS voltage making the ECU thing you have your foot on the gas.

[mntllycrzy]

so i need to check from the tps connector to ground? and from the ecu to ground? should i make auxilary ground wires for them?

[Ecomike]

so i need to check from the tps connector to ground? and from the ecu to ground? should i make auxilary ground wires for them?

Yes. I have run several new grounds on mine, so have most others here with Renix jeeps. Any ground wire that has more than 1 ohm from the test point to the battery negative post is a problem.

[mntllycrzy]

ok, i will have to work on this monday on my day off.

[kc9afz]

new here but old problem bought my mj in 1988 can anyone tell me how much vac should be at the map when i unplug the vac line from my map and let the idle come down and then plug it back in it will idle fine until i shut it down. it will also idle fine when i first start it cold but only until i shut it down.

[Jeepie]

We had this exact same problem with our '90 4.0 5sp. Replaced everything twice TPS, CPS, IAC, etc. etc. - still the same high idle.. 2000 RPM's+

The solution ended up being to replace the EGR valve and EGR valve selenoid. (sp?) There was a small tear in the EGR valve causing a vacum leak and as soon as that was replaced the high idle problem went away and never came back.

Hope this helps..

Jeepie

[88 Wagonman]

Deleted by Administrator.

http://www.naxja.org/forum/showthread.php?t=59881
I don't mean to be a nag, I just don't want to see this forum shut down over a stupid law suit.

[Ecomike]

We had this exact same problem with our '90 4.0 5sp. Replaced everything twice TPS, CPS, IAC, etc. etc. - still the same high idle.. 2000 RPM's+

The solution ended up being to replace the EGR valve and EGR valve selenoid. (sp?) There was a small tear in the EGR valve causing a vacum leak and as soon as that was replaced the high idle problem went away and never came back.

Hope this helps..

Jeepie

That is one high idle cause (vacuum leak) most of us have failed to check on or even think of. Good point!!!!! It is also one that is easy to diagnose and test!

:clap:

[SoCal88XJ]

Maybe someone pointed this out on some page previous to this post, but I found my high idle problem finally n my 88 XJ. The fuel pressure regulator on the front of the fuel rail to the injectors had began leaking fuel accross the internal diaphram and into the vacuum system. You can pull the vacuum plug on the fuel pressure regulator while it is running and see wet fuel (easy test). This was causing intermittent hard start, high idle when cold that flipping with the heater/ac would correct occationally, poor or erratic warm idle and a lack of overall performance. I swappedit out, all of those problems went away. Easy to test, $44 neihoff replacement from Kragen auto Parts and fairly easy to replace (torx bolts a little hard to get to underneath). I hope this helps others too, it really drove me crazy looking for it!!!

[k.smith904]

Oh yeah, I'm bringin this thread back.

So I've had some no-start and stall-out problems lately with my 87 4.0 and I've read about having to meticulously clean the grounds, but my engine bay is a jumble of wiring, so if someone has the spare time, can you take pictures of the ground locations in a renix, or describe them very specifically?

'Preciate it.

-Kev

[89xj]

Oh yeah, I'm bringin this thread back.

So I've had some no-start and stall-out problems lately with my 87 4.0 and I've read about having to meticulously clean the grounds, but my engine bay is a jumble of wiring, so if someone has the spare time, can you take pictures of the ground locations in a renix, or describe them very specifically?

'Preciate it.

-Kev

no start and stall out is a sign of a bad cps. if not cps, fuel delivery(fuel pump, fuel filter...) or bad coil.

as for the grounds:
negative battery terminal to side of block
ground strap from head to fire wall
ground from main wiring harnes to drivers side fenderwall. on my 89 its right in front of windsheild washer fluid resivoir.
there are also grounds to the tps and map sensors.

[88xjchief]

Today I went to check my tps and found no voltage in C and B terminals. I have 4.85v in A and B terminals. I hooked it up to a scan tool and it said for tps 0 volts. Could it be a bad tps?

[Ecomike]

Today I went to check my tps and found no voltage in C and B terminals. I have 4.85v in A and B terminals. I hooked it up to a scan tool and it said for tps 0 volts. Could it be a bad tps?

Disconnect the TPS, retest the wires in the wiring harness to see if the short is in the wiring harness.

Sounds like A & B wires are shorted, but your statement is conflicted concerning the B terminal.

[PuddinHead]

I SUSPECT SOME OF THE AFTERMARKET TPS UNITS HAVE THE WRONG VARISTER RESISTANCE VALUE. IF YOU TEST THEM USING AN OHM METER, YOU CAN SEE THE RESISTANCE CHANGE AS YOU MOVE THE LITTLE ARM, BUT IF THE TOTAL RESISTANCE IS WRONG ACROSS THE POT, THEN THE VOLTAGE THE COMPUTER SEES COULD BE HARD TO SET.
IN OTHER WORDS IT IS EASIER TO DIAL IN THE RIGHT SETTING ON A 100 OHM VARISTER THAN ON A 1000 OHM VARISTER ESPECIALLY IF THE FACTORY SPEC IS FOR A 100 OHM UNIT. OLD MAN RENIX IS SO PARTICULAR.

JUST AS LIKELY THOUGH IS THAT THE WIRING GOING TO THE CPU FROM THE TPS IS CORRODED SOMEWHERE. THIS WILL ALSO MAKE CALIBRATION NEAR TO IMPOSSIBLE.

IN THE FINAL ANALYSIS PITY THE POOR FOO WHO DRIVES A RENIX. AX ME HOW I KNOW...:D

[renixmike]

good luck with that one dood. been at war with that one for about a year now.

[Muad'Dib]

I was plagued with the High Idle Curse again... and now i have a few questions.

This particular time, i couldnt get the idle to come down until i unpluged the TPS at the flat plug which i believe is to the ECU. Once unplugged, everything was back to normal. When i pluged it back in, the high idle was back.

This brought up some questions.. First of all, WTF is the ECU side of the TPS for then anyway? When unplugged i saw no difference in drivability of the Jeep compared to a normal working TPS adjusted correctly.
The reason i ask, is because i for a long time failed to believe that my TPS was the cause of a high idle. Reason being is because i swaped it out with about 5 different TPS's from the Junkyard. I figured there was no way that 5 TPS's caused the same problem in different ways. I am now about 98% convinced that all the TPS's that i have tried were either bad or failing. I have yet to try a new one. Is it possible that there is something wrong with my ECU?? Any Suggustions here would be appreciated.


On another note:

I have always read and heard that when adjusting the TPS, you want the output voltage to be approx 82-83 percent (it varies source to source) of the input voltage.
So if your input voltage is 4.65 volts, your output voltage should be adjusted to ~3.85 volts.
I have always followed this rule until i was reading my Factory Service Manual. In the FSM for a 90, it says to check the input voltage and it should be approx. 5volts. If it is, then adjust the output voltage to be 4.15 volts.
As you can see it doesnt say anything about relating your output voltage to your input voltage. It only says to make sure your input voltage is close to 5, and adjust your output to 4.15 period.
So last night when i changed out my TPS (yeah with another one of those 5 TPS's that i have laying around) i went ahead and adjusted it to 4.15 volts per my 90 FSM.
So far, i notice absoloutly no difference than before when i have adjusted the TPS to be 83% of the input.

[Ecomike]

Almost sounds like your wiring from TPS to ECU has a problem. I can not drive mine with the TPS disconnected. If I give it gas with no TPS connected to the ECU it bogs down and back fires. Also sounds like all those used TPS's may have problems. I would also look for the source of the voltage drop from the ECU to the TPS. The ECU has a 5 volt output to the TPS, and the return voltage to the ECU from the TPS tells the ECU where the throttle is at so it can estimate increased or decreased air flow before it gets to the O2 sensor. It speeds up throttle response .

[Muad'Dib]

Almost sounds like your wiring from TPS to ECU has a problem. I can not drive mine with the TPS disconnected. If I give it gas with no TPS connected to the ECU it bogs down and back fires. Also sounds like all those used TPS's may have problems. I would also look for the source of the voltage drop from the ECU to the TPS. The ECU has a 5 volt output to the TPS, and the return voltage to the ECU from the TPS tells the ECU where the throttle is at so it can estimate increased or decreased air flow before it gets to the O2 sensor. It speeds up throttle response .


Now im very concearned about the ECU side of the TPS. Cause as i said, i unplugged it, and everything was great.

Ecomike, when i was stating the voltages, i was talking about taking the normal readings from the TCU side of the TPS. From what i have heard and read, 4.65 volts is fairly normal for a Jeep 18-19 years old.

Do you have any suggestions for me to check out the ECU side and its wiring??

[Ecomike]

Now im very concearned about the ECU side of the TPS. Cause as i said, i unplugged it, and everything was great.

Ecomike, when i was stating the voltages, i was talking about taking the normal readings from the TCU side of the TPS. From what i have heard and read, 4.65 volts is fairly normal for a Jeep 18-19 years old.

Do you have any suggestions for me to check out the ECU side and its wiring??

My 87 and 89 both read about 5.00 volts +/- .02 volts on a high quality meter. Check the output voltage at the ECU itself.

The TCU side has no effect on idle, only the ECU side affects idle. That is why I preached in this thread about the need to check both sides of the TPS, including the 5 volt input to both sides, the ground on both sides, and the TPS span for high, low and smooth operation. Some have report getting by OK with a 4.65 volt input, but what if your input is jumping around due to a poor contact in the harness, and reading 4.95 one second then 4.5 the next on the input to the TPS on the ECU side?

I check both live voltages, and then check wire resistance (using a very long set of leads) with the power off to try and isolate problems.

Is your O2 sensor working? Is it getting into closed loop operation? When I disconnect the 87 ECU side of my TPS it will back fire if I stomp on the gas in park. Have not tried on the 89.

[Muad'Dib]

My 87 and 89 both read about 5.00 volts +/- .02 volts on a high quality meter. Check the output voltage at the ECU itself.

The TCU side has no effect on idle, only the ECU side affects idle. That is why I preached in this thread about the need to check both sides of the TPS, including the 5 volt input to both sides, the ground on both sides, and the TPS span for high, low and smooth operation. Some have report getting by OK with a 4.65 volt input, but what if your input is jumping around due to a poor contact in the harness, and reading 4.95 one second then 4.5 the next on the input to the TPS on the ECU side?

I check both live voltages, and then check wire resistance (using a very long set of leads) with the power off to try and isolate problems.

Is your O2 sensor working? Is it getting into closed loop operation? When I disconnect the 87 ECU side of my TPS it will back fire if I stomp on the gas in park. Have not tried on the 89.

My 02 Sensor is working correctly... but im assuming this only because i just replaced it less than a couple months ago. As far as i can tell it gets into closed loop.

Can you give me an idea on where to look in my FSM for information on the ECU side of the TPS? Or do you happen to have a cheat sheet on what needs to be checked where.

Im thinking its time to check the readings at the ecu to see what its seeing and outputting. The ECU side just has Input, output and ground right?

I also wonder if the ground for the ECU side of the TPS is important to be good at the ECU, or if its ok just to have a jumper at the TPS. The same goes for the TCU side. Does this make since?

For example, lets say that the ground wires for both sides of the TPS are weak\corroded, or split (higher than normal resistance). If you put a short jumper to ground at the TPS, then you get a good ground at the TPS, but is it important that said grounds are good at the TCU\ECU respectively...???

[Ecomike]

First off it really sounds like you need to read (and take notes) this thread cover to cover. Most of your answers are right here.

Both sides of the TPS, and the ECU have separate ground wires. They are all important and significant. I have had to replace the TPS ground on both sides of mine, and on the TCU so far.

[Muad'Dib]

First off it really sounds like you need to read (and take notes) this thread cover to cover. Most of your answers are right here.

Both sides of the TPS, and the ECU have separate ground wires. They are all important and significant. I have had to replace the TPS ground on both sides of mine, and on the TCU so far.

I have skimmed through this thread many times. Unfortunatly i just dont have the time to read and take notes to find what could easily be consolidated into one decent post... especially from the people who probably have the information off the top of their heads.

Ill have to take another look at this problem at a later date when i have more time.

[Ecomike]

I have skimmed through this thread many times. Unfortunatly i just dont have the time to read and take notes to find what could easily be consolidated into one decent post... especially from the people who probably have the information off the top of their heads.

Ill have to take another look at this problem at a later date when i have more time.

I had it off the top of my head once, but it's now buried and scattered about in this rather short brief thread, LOL. :laugh:

And the summary you speak of simply leads to another dozen detailed questions and issues that you already asked and that are already answered here. I beat on the Renix TPS issue, high idle problem, for over a year, documented my ideas, thoughts and tests and results in the earlier parts of this thread.

I understand not having the time. Take my word for it, if you don't have time to scan this thread for my more pertinent posts, you don't have time to track down the high idle TPS and related gremlins either.

I followed other posts from here and there including NAXJA posts and links from here, and I still spent a year fighting the damn thing before I finally fixed all 6, or was it 8?, things that were all contributing to the random, high idle on mine.

As I said in the prior post, the first thing you should do is check the wires, point to point for continuity, all 6 of then from the TPS to the ECU and the 2 ground wires, and then check all the ECU grounds at the ECU. All grounds should read less than 1 ohm between the ground connection / wire and the Battery negative post. Be sure to wiggle wires and the wiring harness during ground and continuity tests. I have found bad ground wires and replaced the wires, 2 on the TPS (I ran the new ones straight to the battery Neg post), and one on the TCU just on my 87. Then the TPS and IAC also were bad, as were many CCV lines.

Once you have done that (checked all the wires), if it still acts up I would buy a new TPS in your case.

[Muad'Dib]

I stayed up late tonight to read this thread in its entirety. I found great information on what to check on the TCU side, but absolutely nothing on the ECU side. I'm talking about pin outs. Id like to pull the ECU out and check reading there as i am going to do at the TCU now that i have the proper information from here (http://www.transonline.com/transDigest/magazines/1997-10/Shift%20Pointers/index.html) on page 4. I guess ill have to resort to my FSM.. sometimes shit is just to hard to find in there!!

[Ecomike]

You do have the Renix Fuel Injection manual right?

I posted data in this thread on the ECU side of the TPS, actual ohm readings, mounted and unmounted, for WOT to idle positions (Power off, wiring harness disconnected) readings, about 2200 to 6600 ohms, respectively IIRC. The Renix Fuel injection FSM has the WOT to idle voltage readings for the ECU side, which should read about .83 volts at idle and about 82-87% of ECU input voltage at WOT on the third return wire from the TPS to the ECU at WOT. The lundford (IIRC, ? SP) web site has a nice brief on the TPS pin outs, and Renix Fuel Injection manual has the ECU pin outs and values, and the TPS pin outs.

When checking my TCU I had to replace one bad ground wire and one 12 volt unfused wire that keeps the TCU memory alive when the ignition is off.

[Muad'Dib]

I found what i was looking for in the Electrical Section of my FSM (which is a whole other book).

It shows that most of the sensors grounds splice off of one from the ECU... which most of us already knew was true for the TPS.

I may have to scan and post the 3 important pages that i found.

Interestingly, the ground splice also runs to the diagnostic connector under the hood. This (from looking at the schematic) would be a great place to also check for a load, and or high resistance. IIRC it was pin 8 on the bigger connector (Right smack dab in the middle). I feel it would be a good quick test to see if its a ground problem, or if you should start digging deeper into the +5v supply.

At first i though it showed the +5v for all the sensors coming from one splice, but i was wrong... it appears that they each have a seperate wire going to the ECU.

I dont remember which pins on the ECU are for the TPS, but i will scan those pages tonight and post them.

[Ecomike]

Keep in mind that wires have been known to fatigue and break, connector female pins get loose and dirty. While you may get a good reading at one end of a ground, or voltage input, or return, it can degrade along the return path. So a good signal or ground at the diagnostic connector may be miss leading!

Don't assume anything as you run the tests.

I have preached before I will do it again, that the best time to do tests is during the random gremlin malfunction!!!!

[PuddinHead]

About 80% of electronic failures/problems are wiring related whilst the remaining 20% is component related. If a problem is intermittant that just screams wiring to me. Running new wires back to the ECU could cure a host of engine problems related to sensors. Wiring can look good and even test good with a standard volt-ohm meter, but still be corroded inside the jacket.:lecture: When dealing with these small DC voltages this kind of corrosion would change current flow nearly all the time.

[Ecomike]

About 80% of electronic failures/problems are wiring related whilst the remaining 20% is component related. If a problem is intermittant that just screams wiring to me. Running new wires back to the ECU could cure a host of engine problems related to sensors. Wiring can look good and even test good with a standard volt-ohm meter, but still be corroded inside the jacket.:lecture: When dealing with these small DC voltages this kind of corrosion would change current flow nearly all the time.

Surface wire corrosion inside the wire by itself is not a problem in my book, but many have reported spots in the wiring where hidden taps have loosened, and where all but one or two threads of multicore wire are fatigued and broken leading to voltage looses. I can also see large ground wire problems causing feed backs into the TPS ground when head lights, brake lights, other large loads are dumped to a poor overall grounding system in the XJ body.

[Muad'Dib]

Sorry for the delay, here are the two schematics i found to be helpful:

http://www.jeepstrokers.com/TPS and ECU Wiring Diagrams 1990 FSM.pdf

[doodahman]

I fixed my high idle problem. The 2 rearmost nuts were slightly loose on my manifold. All of a sudden, it started ticking and when I tightened them, voila, no more high idle. Stupid vacuum leak.

[CJR]

I had this problem awhile ago. It turned out to be a cracked intake manifold that the previous owner had cleverly covered with aluminum epoxy. The epoxy perfectly matched the aluminum manifold and I never saw the crack. My son's sharp eyes picked it up. As the manifold heated up, it would separate behind the epoxy and cause erratic vacuum leaks and high idle. Once I replaced the intake manifold, the problem went away. Hope this helps.

Best regards,

CJR

[Muad'Dib]

Well to update, i pulled the TCU, and tested the TPS wires and they all passed with flying colors. So did the wires for the ECU side. I went ahead and installed a ground wire at the TPS for the ECU side for safe measure just as i have already done for the TCU side.

Voltage from the TCU is the same at 4.66V (at both directly at the TCU, and after the wiring to the TPS). Voltage from the ECU is 5.05v.

For shits and giggles i also checked the other ECU +5v outputs (to the MAP sensor for example), and i got very close readings. They were all over 5 volts (on average 5.05 volts).

Given the facts above, it made since that something was up with my TCU. I checked the input voltages to it (switched and unswitched +12 volts), and they were spot on.

At that particualar time i installed another TPS i had laying around. It cured the idle issue, but some other weird things started happening. My "RPM Float" came back. It would sometimes act like it was staying in gear too long.. just normal weird i know ive got a crappy TPS problems...

I dealt with it unit i could finally convince myself to just try a new TPS. I got it from Rock Auto. Its an Airtex brand. Model number 5S5212 (http://www.rockauto.com/dbphp/prt,903,5S5212). The nice thing about this TPS from Airtex is that it came with new hardware. They were phillips head screws. Instead of those old torx ones from the factory. One big thing i did notice before installation was that when moving the arm on the TPS, it was much stiffer than any other one i have touched before.

I installed the TPS, and adjusted it to output 4.15 volts to the TCU per my 1990 FSM.

I took it for a quick drive tonight, and all seems perfect. No more problems with the high idle (which i expected)... but was surprised me even more was the was the throttle response changed. I cant say it was in a good or a bad way, but it was definetly different. Another problem it fixed that i have dealt with for awhile was something i describe as "RPM Float". After acceleration, if you let off the gas and just let it coast, the tach would drop to about 1,000 RPM's, and then Jump up to about 1,300 RPM's. It would cycle like this until you slowed down enough, or accelerated again. You could hear the engine rev when it was doing this also. Like you were giving it a slight amount of gas when you really werent. Anyway, its nice to know what was causing that problem.

Now only time will tell if i get some weird problems again or not. Now that i have a new TPS for the first time since i have had the Jeep, if a problem arrises, then i think im going to try a different TCU that can output close to 5 volts to the TPS and see what happens then.


I hope what i have written here helps someone in the future.

[The Lure Washer]

Hey Mods Can we get a sticky!@

[Ecomike]

Nice update and detail, you are officially awarded one ataboy!:yelclap:

I suspect a hand full of us could fill a book with a list of weird things and symptoms a goofy, used, but not totally dead TPS can cause. Now you have me wondering if TPS is not off just enough to be causing my final still a little low on MPGs and not quite full power output effects.

Sounds like you got the beast fixed for now! Congrats.

[roktoy]

Guess I’ll bump this great thread back to the top…….

First, let me say that this is my first forum post here and I want to thank Ecomike and others that have contributed to this thread…..it’s been very helpful.
I just purchased an ’89 XJ with 4.0L & AW4. It drove fine initially but when it warmed up after a few minutes of driving, the tranny would no longer shift out of first (and the idle was running high). I did a little research on here that led me to suspect the TPS may be bad.

I measured the impedance on my TPS (warm) and got these readings:

TCU Side:
Pin A to B: ~6.6k (idle) to ~2.4k ohms (WOT)
Pin A to D: ~200 ohms, constant
Pin B to D: ~6.5k (idle) to ~2.3k ohms (WOT)
ECU side:
Pin A to B: ~47 ohms, constant
Pin A to C: ~2.4k (idle) to ~3.6k (mid) to ~2.4k ohms (WOT)
Pin B to C: ~2.4k (idle) to ~6.3k ohms (WOT)

It appeared I had some internal shorting and other issues, but the readings were erratic as well. This pretty much convinced me the TPS was faulty, so I decided to replace it. I bought an Echlin one from Napa for $45. Before I installed it, I decided to check its impedance to see how a new one compared. I measured:

TCU Side:
Pin A to B: open circuit, constant
Pin A to D: open circuit, constant
Pin B to D: open circuit, constant
ECU side:
Pin A to B: ~4.0k ohms, constant
Pin A to C: ~6.3k (idle) to ~2.4k ohms (WOT)
Pin B to C: ~2.3k (idle) to ~6.4k ohms (WOT)

It seemed odd to me that the TCU side measured open between its pins and a little further looking on this forum led me to this thread and Ecomike’s measurements showing the TCU side was a second reverse pot. I returned the first TPS to NAPA and got a replacement. The second unit measured:

TCU Side:
Pin A to B: ~2.4k (idle) to ~6.5k ohms (WOT)
Pin A to D: ~4.1k ohms, constant
Pin B to D: ~6.5k (idle) to ~2.4k ohms (WOT)
ECU side:
Pin A to B: ~4.0k ohms, constant
Pin A to C: ~6.3k (idle) to ~2.4k ohms (WOT)
Pin B to C: ~2.3k (idle) to ~6.4k ohms (WOT)

All seemed right with this one. Goes to show that you probably need to check a new sensor before installing it. I have a habit of checking parts most times anyways (brake cylinders, starters, alternators, etc.) before installing them on a vehicle to save possible headaches later.

I installed the new TPS. I also checked the ground wires for the ECU and TCU and found them to be floating up to nearly 0.7V. I added a temporary ground wire over to the battery negative terminal and the idle sounded a bit better, so I took it for a test drive. All tranny gears had returned. It shifted and drove fine.

After my test drive, the idle was still a bit on the high side but I was pretty pleased with the progress. I took the ground wire I had simply wrapped around the negative battery terminal off and soldered on a lug. I placed the lug under the ground bolt on the firewall. This time when I fired up the motor, the idle was near normal speed and smooth. Seems this minor improvement in grounding made some significance as well. I plan to go over the other grounds when I get the chance.

I once again checked the old TPS I had removed and was getting readings that were pretty close to normal. So…I stuck the old TPS under the hood on the hot engine to heat soak for about 10 minutes. After that time, I rechecked the TPS readings. They were not identical to the previous warm readings, but they were still flaky. Seems that in my case, the TPS operation went south as the unit got hotter.

I next decided to cut the TPS open. Maybe someone has done this before, but I had not seen it. Inside, a small plastic drum rotates in the outer housing. On the drum are small metal fingers that rub against resistor material on a small flexible circuit card that is curved inside the outer housing. Evidently these parts mechanically wear and result in poor contact or maybe loose foreign debris plays some havoc with the resistor values.

In any case, thanks much to everyone that’s contributed to this thread. It has been immensely helpful and I now understand a lot more about this system. Maybe my story can add to this thread and help someone else down the road.

Jay

[Mudweiserjeep]

Welcome aboard roktoy! Very well written. Lots of good info.

Thanks - Tim

[Athompson]

reading through this thread just gave me lots of info i have been looking for....rpm's "jumping"...idle issues galore...

[Ecomike]

Great old threads never die, LOL. Glad it has helped. Interesting to hear of the heat effect too!!!! Most interesting

Got any pictures of the dissected TPS?

I had a brand new IAC that was bad right out of the box 2 weeks ago.

[eswjeep]

I used to change that damn IAC every six months or so on my 90. That was the one thing about that jeep that made me insane. Now I 've got a 96.

[xytrix01]

Hi all!

I've had the intermittent high idle issue for quite a while now, and frankly i've just been ignoring it. Until recently it was usually fine, and would only act up sometimes. Well recently its started to be a more often than not problem, and of course it would because my smog check has just come due! Of all the rotten luck!

I tried a whole list of things from this thread including replacing/upgrading all the grounds and testing all the sensors. No change. I reset the TPS to .815VDC. No change. I replaced the Idle air control motor. No change.

So I started looking elsewhere, and I just have a quick question.

In the photo below, is there supposed to be any vacuum coming through the little hole at the bottom of the photo? When I block this little hole, the idle drops down to ~800rpm or so and if I put my finger over the hole for the IAC I can feel little pulses as it adjusts to let a little more or less air in. I turned the torx screw on the side of the TB to shut off the litttle passage, but it's nagging me because it seems a screw would cause a constant high idle, not an intermittent one... I kept track of how many turns i shut it in case i have to put it back.

http://farm5.static.flickr.com/4115/4862386412_e1cb1e3c3f.jpg

[joe_peters]

Check your EGR valve for sticking.

[xytrix01]

Like sticking shut or not opening? when I rev the engine I can see the little pin between the vacuum diaphragm and the egr move, and if I manually pull back that pin the engine bogs down and runs like poo. I don't think it's stuck... *shrug* I'll try to post a list of everything that I have already done to it tomorrow.

[xytrix01]

Also, I notices that my ECU says "Bendix" on it, not Renix... Are they the same thing?

[gradon]

Renault + Bendix = Renix

[Ecomike]

Sounds like you have a vacuum leak now. I would look everywhere there is a vacuum line for even the smallest leak!!! Once all the leaks are fixed then you can deal with calibration. I would suggest pulling and cleaning the inside of the throttle body with carb cleaner, then reinstall with a NEW gasket.

I actually had a brand new IAC fro Autozone that was defective right out of the box 6 weeks ago!!!! So look into that possibility too.

Once you have all the vacuum leaks fixed (even the valve cover gasket needs to be air tight), then you calibrate the idle air screw (torx) on the throttle body side that you mentioned. It does not take much trash inside the throttle body. carbon build up, to cause IAC travel problems that make a fast idle.