RENIX help - random high idle TPS out of adjustment

OK so it's been doing the random high idle thing for awile. Start the Jeep it idles at 2K+ rpms for sometimes as long as a couple minutes then slowly returns to normal. Started with the previous owner. He changed the MAP sensor and IAC motor. I now have it and it's been something I want to fix but it hasn't done it in awhile so you forget about fixing it... So I install a bored TB and spacer and transfer the IAC and TPS to the new TB and figure I should set the TPS to the correct adjustment. Find the procedure in the FSM, get the meter out and adjust the TPS to spec.

Bad idea! Input voltage is 4.72vdc, the manual says if you don't have 5.0vdc input voltage then you sent the output voltage to 82% of the input or in my case 3.87vdc. Start the Jeep and it idles at 3800rpm and will not come down. Hmmmm... So out with the meter again and start experimenting with various TPS output voltage settings, increasing voltage in .10vdc increments. The only way to get it to idle (below 3000 rpm) is to set the output voltage to 4.35vdc or higher. OK so the TPS is "bad". Off to NAPA get a new one, install it, adjust it to spec and it idles at 3000 rpm. UGH! I skip the experiment phase and go back to 4.35vdc output voltage and it idles normal.

But wait there's more, At the high TPS output voltage it has a surge at idle and a very noticeable bog when you zip the throttle. So being the tinkering kind of guy I am I set the TPS to factory spec with the engine running (although the FSM says not to do that) and the idle smoothes out and the throttle response is crisp. Shut it off, and on the restart it goes back to the 3000 rpm idle. Pissed off now, back to NAPA and get a CPS, the only sensor left that I can think of and change that. No effect on the idle.

The only way to get it to idle is with a high output voltage adjustment on the TPS.

My assumptions are as follows:

1) the TPS decreases in output voltage as throttle position is increased. This leads me to believe that with the high TPS voltage setting I am running very lean at idle. Which makes sense as the idle is surging and it has a bog of idle.

My questions are:

1) is there a pressure port on the fuel rail to test fuel pressure? if so what is spec on it?

2) anybody know how the RENIX computer actually works? can you still get one?

3) what other inputs to the ECM have effect on fuel delivery? Temp sendor and knock? Knock is more a function of timing though...

Background info on this Jeep. 1990 model. 198,000 miles, tired but still runs well (other than this idle thing)

Got any ideas?


Bob

Bob...

The guy to talk to about this is Don (digger) from the .org board. He's really good with this kind of stuff and is a wealth of knowledge with numbers.

you might check with him when you get a chance.

I'd like to know as well....seems I'm experiencing the same issues.

If I set the TPS with the engine running to the stock spec it runs great...turn it off and it idles high on restart. Set the TPS with the key on and the engine off and it idles decent (sometimes high) at startup with a light "hunting" but bogs slightly at quick throttle.

First off the TPS is actually a two part TPS (or two TPS´s) a sandwhich. The side your adjusting is the tranny (TCU) side 4 pin. The inside three pin is for the ECU (Engine control module or unit), you can check it just like you would for a stick shift.
The ECU side of the TPS and the TCU side of the TPS, get there base (supply voltage from the TCU and the ECU seperatly). So you are actually trying to adjust the two together, with two different inmput voltages and actually seperate grounds. When checking and adjusting, it´s probably better to adjust with the TPS grounds 3pin and 4pin and NOT to the chassis.
Check and see if the throttle plate is pretty much fully seated and no one has been adjusting the throttle stop, first. The throttle plate on the TB´s I´ve looked at is almost a pefect seal in the bore, seems the throttle stop is probably just to keep the plate from slapping the bore. Somebody had bent my throttle stop, sometime in the past.
Lots of places for there to be resistance in the wires that will screw up your values. Try checking the 3 pin ground wire for voltage (ignition on, motor not running) from the wire to chassis ground, this may be an indicator of standing voltage , which equals resistance in the ground circuit, (there is bound to be a little).
The TCU side of the TPS, starts with a high initial setting, 83% of supply voltage and the the adjusted voltage drops as the throttle is opened. The ECU side of the TPS, works just the opposite, it starts with a low inital voltage (ideally the 17% of your 83%) and rasies as the throttle is opened.
* Check and see if you don´t have the TPS arm on the wrong side of the throttle arm.*
The low (adjusted 17%) voltage in the ECU side of the TPS is often .6-.7 volts, think ideally it should be .8 volts, by the book. The ECU adjusts to compensate for different baseline voltages somewhat.
The TCU side is typically close to 4 volts baseline (83%) , often a little lower, depending on imput voltage. Actually your supply voltage to the TCU side of the TPS is quite high, they often average around 4.6-4.7.
If this confuses the heck out of you, don´t feel lonely, me too.
Reason I mentioned the TPS arm was, I seem to remember, trying the TPS arm once, with the TPS removed from the TB, the wires hooked up and the motor running, I twisted the arm by hand (curious) and the idle went way up (like oh chit high). Leads me to believe the higher the 3pin TPS base line voltage the higher the idle.
The TPS, the MAP sensor and other sensors are on kind of a daisy chain. And not independant. I haven´t researched this much, just remember it from looking at the wiring diagrams.

Bender said:

I'd like to know as well....seems I'm experiencing the same issues.

If I set the TPS with the engine running to the stock spec it runs great...turn it off and it idles high on restart. Set the TPS with the key on and the engine off and it idles decent (sometimes high) at startup with a light "hunting" but bogs slightly at quick throttle.

Click to expand...

I´ll try to help, been through the same thing, pretty much, but I´m having brain lock right now (need to get outside for awhile). I´ll get to you later and/or you can PM me and I can maybe give you some tips.

Take a look at the intake manifold bolts, they might be are loose. Torque them down and it will back to normal. I had the same problem. I adjusted the tps, cleaned the tb and iac. replaced the iac and tps, tested every sensor on the engine.

Try it
Katarn

8Mud, what are the pin outs for the ECU (3pin) connector?

Bender said:

I'd like to know as well....seems I'm experiencing the same issues.

If I set the TPS with the engine running to the stock spec it runs great...turn it off and it idles high on restart. Set the TPS with the key on and the engine off and it idles decent (sometimes high) at startup with a light "hunting" but bogs slightly at quick throttle.

Click to expand...

Same deal here, except at the factory spec it will not idle below 3K...

Update:

Tested voltages again.

TCU Input = 4.72vdc Output = 4.35vdc
ECU Input = 4.92vdc Output = 243.8 mvdc (milivolts)

Thats way low. The FSM for the manual tranny states 17% of input, so that would be .78 vdc. Off to adjust again, back in a bit...

The TPS is a screwy thing.....

The idle seems to adjust around it somewhat.

My input is 4.75V

If I set my TPS up to about .81 volts (manual tranny style) which is 17% my idle will be around 500 rpms fluctuating 100 rpms or so. My throttle response isn't great with a bit of a hickup when I first hit give it throttle.

If I set my TPS to .75 volts which is 15.7% my idle will initially be really high but after turning the truck on and off a couple times it seems to re-learn and set the idle about 900-1000 rpm's. the throttle response is quicker

If I set my TPS to .67 volts which is 14% (recommended by some as the best setting) my idle again will be high initially but after turning the truck on and off and taking it for a spin it again settles down to about 900-1000 rpm and there is no hickup at all when the throttle is first depressed.

So, it seems sometimes the system adjusts to the TPS and sets the idle lower and sometimes it doesn't. Makes me wonder the role the TPS really plays in the system alltogether.

As I suspected with the ECU side of the TPS adjusted to spec the idle goes through the roof 3200rpm today. While at the correct 16% setting I checked the TCU side of the TPS and it's in spec as outlined in the FSM...

Adjusted the TPS engine running to spec, it idles smooth, at correct speed and throttle response is very crisp. Shut it off and restart and idle speed goes to 3200 rpm.

Throttle plate is closed, completely. The stop screw is adjusted only to take the slack out.

I'll check torque on the intake next...

Bender said:

The TPS is a screwy thing.....

The idle seems to adjust around it somewhat.

My input is 4.75V

If I set my TPS up to about .81 volts (manual tranny style) which is 17% my idle will be around 500 rpms fluctuating 100 rpms or so. My throttle response isn't great with a bit of a hickup when I first hit give it throttle.

If I set my TPS to .75 volts which is 15.7% my idle will initially be really high but after turning the truck on and off a couple times it seems to re-learn and set the idle about 900-1000 rpm's. the throttle response is quicker

If I set my TPS to .67 volts which is 14% (recommended by some as the best setting) my idle again will be high initially but after turning the truck on and off and taking it for a spin it again settles down to about 900-1000 rpm and there is no hickup at all when the throttle is first depressed.

So, it seems sometimes the system adjusts to the TPS and sets the idle lower and sometimes it doesn't. Makes me wonder the role the TPS really plays in the system alltogether.

Click to expand...

Sometimes takes a few days for it to settle in. How are you adjsuting your idle, around 800/850 works for me, high enough to keep the alterantor charging, not so high to lurch when shifting into gear, may have some affect on long range tranny clutch wear at stops. I just changed my 02 sensor, for my motor, hunting at idle. I´d checked everything else, just got everything where I wanted it and my CPS crapped out, put in a new one and the idle changed again, but only a hundred RPM´s or so. I´ve said before, there are so many inputs for the idle program, it´s a wonder it works at all. One guy said he caught his idle at the proper place and unhooked IAC, fast, been fine ever since :laugh3: Sounds like what I went through with my old carburated YJ, same guy must have written the programs.
Random, high idle at start, for a few seconds, is typical. Don´t know of anybody that has successfuly found a cure.
14 percent also worked well for me, but I´ve since set it back to the 83/17 ratio, or as close as I can get, with two different input voltages. Mileage issues, which a TPS adjustment didn´t seem to help at all.
I went through all my grounds a long time ago, the ones on the dipstick holder are important and also the block to firewall.

I am driving around with my IAC disconneced once the engine found the right idle one of these days i am going to trouble hsoot it but i honeslty think on mine its a bad ground or a C101 issue... the 89 does not have the c-101 issue but we are talking a total of what 3 wires going to the ECU from the TPS on the engine side (not the tranny side) my idea is to rerun new wires to the ecu from the tps directly and see if that fixes my prob but for now the IAC is disconnected

Rock Yacht said:

As I suspected with the ECU side of the TPS adjusted to spec the idle goes through the roof 3200rpm today. While at the correct 16% setting I checked the TCU side of the TPS and it's in spec as outlined in the FSM...

Adjusted the TPS engine running to spec, it idles smooth, at correct speed and throttle response is very crisp. Shut it off and restart and idle speed goes to 3200 rpm.

Throttle plate is closed, completely. The stop screw is adjusted only to take the slack out.

I'll check torque on the intake next...

Click to expand...

If you unhook the like 3/8" major vacuum line at the rear fo the intake, on my motor the idle goes up only to 1500 or so.
If your problem is vacuum, it´s major and you´ll hear it, put your ear on the vacuum booster and check for a major hiss.
Have you done an ohm test on the TPS ground/Black wires with the plugs unhooked? Check them for resistance and shake things a bit, all the way back down the fuel rail to the firewall. There is gonna be a very little resistance, which seems normal.
Anybody who will listen, check the wires running out of the front of the fuel rail, down the front and under the motor, knock sensro, 02 sensor and ECU coolant sensor. Everytime I´ve looked, on most every Renix, there was either heat damage or skuff damage to the wires.

8Mud said:

Random, high idle at start, for a few seconds, is typical. Don´t know of anybody that has successfuly found a cure.

Click to expand...

With the TPS set correctly it's not a random high idle. It's freaking WOT "idle" and it won't come back. I want a stroker in so I let it go for about 20 minutes the other day at 3500 rpm plus. Figured if it blew up I wouldn''t have to fix it. This was with the TPS set to the correct factory settings.

Now I also get the random high idle, I can live with that (for now). Anybody have an idea what's causing the WOT type idle when you set the TPS to the right adjustment?

Checked the intake and all bolts in spec. No vacuum leaks there... Oh and if you cause a vacuum leak by removing a vacuum connection on the intake the normal curb idle speed will increase to about 1500 rpm

Started checking grounds. Ground cable from battery to block toast... Went to the Zone got new cable, opened it when home and some jaskass put a sidepost cable in a top post box...

Harness grounds that attatch in same place ok. Tested TPS signal ground to the stud by the dipstick, one good one bad. The ECM portion of the TPS has a good ground, .02 ohms. TCU portion of the TPS read 11.8 M ohms which for the sake of arguement is an open.

Rock Yacht said:

Started checking grounds. Ground cable from battery to block toast... Went to the Zone got new cable, opened it when home and some jaskass put a sidepost cable in a top post box...

Harness grounds that attatch in same place ok. Tested TPS signal ground to the stud by the dipstick, one good one bad. The ECM portion of the TPS has a good ground, .02 ohms. TCU portion of the TPS read 11.8 M ohms which for the sake of arguement is an open.

Click to expand...

Look close at the ground ring for the TCU at the dipstick, mine was not soldered (the ECU ground was). It was pretty darned green and had resistance. There are other spots, but this was my problem.
Next and I found this by accident, I have an extra motor harness, that I use, to troubleshoot things, I find it much easier to visiualize when I have soemthing to hold.
To get to the point, the input for the TCU side of my TPS was coming from the ECU and the input for the ECU side of the TPS was coming from the TPS. Thought it was a one of a kind screw up, maybe not.
Look at the block to firewall ground, I put another star washer in there and took the paint off of the firewall for a better ground. Don´t actually know how this affects things, but did notice a difference.
Also check the TPS plugs, real close, I had WD 40 on mine, which made a measurable resisitance. I actually had to disconnect the ECU, to isolate the plug and check for resisitance from both ends to the middle. Be thankfull you don´t have the C 101 connector?

New battery ground cable made noticeable difference. Still working on the TCU ground, it's bad somewhere haven't found it yet. Started removing the loom and tape from the harness... What a PIA after 198K miles... Good news is, once the harness is striped I can make a few other modes I've wanted to do for awhile.

My methode is the isolation methode, I break the harness down into pieces and troubleshoot each one.
Might want to check between D-3 grnd from the TPS into the TCU and C-5 out of the TCU to the dipstick ground. The ground out of the TCU may be D-7. Both C-5 and D-7 run to the dipstick ground and exit the TCU. Which one grounds the TPS, I don´t remember, but both ground the TCU and go to the dipstick.
If you disconnect the ground ring for the TCU from the dipstick holder and let it hang in the air, by the diagram you can test C-5 TCU harness pin to D-7 harness pin, with an ohm meter and check for resistance in the bumdle splice, without opening it up. If you do open up the TCU bundle be carefull there is a resisitor tapped into the bundle, not far from the TCU.
A good place to start checking for the resistance to ground, would be the D-3 pin on the TCU, prick the wire and check ohm to chassis. You will probably have to leave the plugs connected at the TCU, but the TPS disconnected. This will tell you, if the resistance is upstream or downstream of the TPS gorund in, to the TCU. Pretty close to the middle of the whole thing.
Look close at the harness connector pins for the TCU, I had a couple that were partially pushed out.
Always be suspicious of resistance at the pins in the harness, the pins oxidize. Di electric grease stops the oxidation, but doesn´t remove it. Also grease, oil and dirt. Spraying the connector with WD 40 or it´s equvilant is chancy, the sesnor circuits are low voltage and it doesn´t take much to screw up the connections and add resisitance.

thanks, maybe this weekend I'll have time to work on it again


Bob