The RenX Files: High idle problems

[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.

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.

 

[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.

 

[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.