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Random high idle kills me!


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My 1989 Renix 4,0 L have a strange behavior from time to time.

 

When started up cold or warm it goes to HIGH ildle 2-3500 rpm with no logic, sometimes when turned of and restarded it's ok sometimes not.

 

Always with the foot on the break pedal , never touch the gas pedal.

 

I have cleand everyting you can think about and checked / fixed the grounding and wiring including conectors.

Replaced the TPS and IAC the Oxygens sensor and no result

New MAP sensor no change.

No loose mainfold bolts

No vaccul leaks found optical or with spraying starter gas

 

I'm out of ideas, and that's a bad feeling ..but worse is the damage to the engine in cold start when the temperature is minus 15 celsius (or 5 farenheit)

 

 

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Engine Coolant Temperature Sensor (ECT) and Intake Air Temperature Sensor (IAT) both have input for engine idle speed. Try disconnecting them, forcing them to their default values and see if idle speed will lower. May take a minute or two.

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I've mentioned this before, and if you've tried all the usual fixes with no success, look into this one.

 

On the Renix 4.0L, the throttle cable doen't run from the gas pedal to the throttle body. The cable goes through the firewall to a bellcrank assembly that's mounted on the frame extension, down beneath the brake reservoir. From the bellcrank, there's a rod that extends up to push on the throttle body. What I've found on my '88s is that dirt and corrosion get into the bellcrank pivot and interfere with free movement. This can cause intermittent high idle. The fix that has worked for me is to spray the bellcrank assembly, concentrating on the pivot, with PB Blaster, while manually pushing on the rod to the throttle body to rotate the bellcrank and work the Blaster into it. That has always fixed the problem for me.

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16 hours ago, SuperSwede said:

My 1989 Renix 4,0 L have a strange behavior from time to time.

 

When started up cold or warm it goes to HIGH ildle 2-3500 rpm with no logic, sometimes when turned of and restarded it's ok sometimes not.

 

Always with the foot on the break pedal , never touch the gas pedal.

 

I have cleand everyting you can think about and checked / fixed the grounding and wiring including conectors.

Replaced the TPS and IAC the Oxygens sensor and no result

New MAP sensor no change.

No loose mainfold bolts

No vaccul leaks found optical or with spraying starter gas

 

I'm out of ideas, and that's a bad feeling ..but worse is the damage to the engine in cold start when the temperature is minus 15 celsius (or 5 farenheit)

 

16 hours ago, SuperSwede said:

Coupla things. 

How did you adjust your TPS?

Have you performed Tip 5 as shown on my website?

Tip 1?

 

16 hours ago, SuperSwede said:

 

 

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Yepp Cruiser, been there, all tips are tested a coulpe of years ago, we have been talking on Jeepforum earlier about the same issues.

 

If you remember I did a total engine overhaul/repair with everything disambled and refreshed or replaced  but just this partikular issue remains the same.

While the engine in comon is running as new. my nick there was Bjorka

 

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I experienced high idle on start up too. My issue was solved between cleaning the electrical connector for the coolant temperature sensor and replacing the ECU with a 1990 ECU from a junkyard Cherokee. I did both at the same time, so I'm not sure which one solved my issue. That said, I don't recommend that you run out and buy a new ECU. It is something to consider if you have another one laying around or can snag one at a junkyard (or as a last resort).

 

I am sure you have done some of the things below a few times:

 

Recommend you check, check, and re-check TPS adjustment.

Clean the throttle body.

Clean the idle air control valve and ports on the throttle body (and then clean some more).

Remove and clean the idle air temperature sensor (the brass thing the screwdriver is pointing at in the photo below). Do it well.

Clean every electrical connector you can think of (TPS, CPS, IAC, IAT, CTS, O2, MAP, ECU, C101....just to name some).

Clean and improve grounds.

 

I feel you. It's maddening.

20181118_103301.jpg

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FWIW, I had a significant high idle issue also. In my case it was a serious TPS issue. The TPS behaved extremely erratically until I resolved my ground issues. In my case it was intermittent. 

I did eventually get it resolved and dial the TPS appropriately (Thanks to Cruiser's guide). 

 

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I get idle issues on my 1989 XJ.  Sometimes it idles very high like yours or barely idles at all, like it is about to stall out.  What fixes it for me is with the engine off, I pump the gas pedal around 10-15 times and that cures my issue for around 6 months. I figure the TPS gets a dirty spot and this cleans it up.

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  • 2 weeks later...

Maybe ...and just maybe ..the problem is solved once and for all but I'm not sure not at all...

 

In lack of anything better to do I took out the power latch relay, the fuel pump relay and the O2 heater relay and run them on the bench a week ago.

 

All three relays worked well in the means that they sounded "click" and switched mechanically when powered with 12VDC, but when checking the internal resistance the contact in the power latch relay was bad. The resistance values should be 0 and ∞ ohm  but was not even close to in any direction.

 

One week later with daily drive and lots of start and stops there's no high idle whatsoever.

I also imagine that she runs smoother and more quiet than before but that could be wishful thinking from me.

 

 

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Glad the problem is solved! 

Curious, did you do away with any of the old relay stuff with the redo on the pass side?

Have any pics of the new wiring pass/driver you could share? :D

On 11/19/2018 at 4:26 PM, SuperSwede said:

I'm pretty sure there is no bad connection in this Jeep, it was some before the overhaul but not as bad as expected.

20181118_160816.jpg

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  • 2 weeks later...

Not really, maybe some of the old junk was removed, to be true the original setup/wiring is a mess from factory and looks like #&!?!& compared to European or Asian cars.

I have  removed the vacuum canister and hoses and some extra wiring from previous owner.

 

The red wiring and fuse boxes you can see have I installed mainly for the extra head lights, extra back lights and the stereo but It also support some original wirings.

 

 

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  • 3 weeks later...

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