The RenX Files: High idle problems

clunk said:

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.

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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 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.

Flash said:

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.

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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:

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.

Ecomike said:

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:

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Flash,

" 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.

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.

efer

Flash said:

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.

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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.

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

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.

langer1 said:

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.

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

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.

langer1 said:

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.

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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.

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, 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!!!!

Hella-XJ said:

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

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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

Greg Smith said:

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

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

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

reelbigdundy87 said:

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

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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).

Ecomike said:

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

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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

reelbigdundy87 said:

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

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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

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

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.

jeepler said:

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.

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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?