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Random High Idle! ugh!


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Hey all! Yet another problem on this troublesome 88' manche. :mad:

 

Anyways, as the title implies, it has a case of random high idles. For example, it could start up fine one minute, shut it down for an hour, turn it on, and then have a high idle while in park. Once you drop it in gear, it will go to a slightly lower idle. However, it will go like a bat out of hell with me NOT on the throttle at all. Not like it's gunning it, but it is definately moving much faster than it should be while i'm not on the gas due to the slightly high idle.

 

The whole thing is, is that it's random. One day it will be great, one day it will idle like crap. Shut it down, restart it, and it will run fine, sometimes it won't. Maybe a sensor? Also, lately, it has been doing the whole, "I don't feel like starting today" thing. As in, sometimes it will start, sometimes it won't. Wait an hour, it will work. And in some cases lately, it took almost 12 seconds of straight cranking to start it, and it will hesitate when starting. Once it's running, it's running though. Never hesitates while driving.

 

I just changed the spark plugs to stock Champions, from the previous owners Bosch Platinums, which I heard are crap for the 4.0. No large difference, if anything, slightly better idle and response.

 

88' Comanche SporTruck 4.0L renix, AW-4, 125k miles, 2wd

 

Any help/opinions would be greatly appreciated! :cheers:

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Did u inspect the TPS and IAC ?

 

No, I actually haven't. What exactly should I be looking for if it was bad? Or do you think they may just be dirty?

 

Also, IIRC, they are both located near the air box, correct?

 

Thanks for the reply! :cheers:

 

They are both mounted in the front of the throttle body.

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Thanks for all the help! :cheers:

 

Is there anything I should be looking for in particular? I don't have any voltmeters or anything :hateputers:

 

Since the change of the spark plugs, it's been running great and hasn't hesitated or failed to start at all. However, it did give me a real high idle once, while in any gear. Hasn't done in since. :nuts:

 

Thanks again for all the help! I'm also going to try and clean out the Throttlebody a bit to see if that helps some flow.

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Thanks again for the replies!

 

Well I took apart and cleaned the IAC, and it had so much grunge and crap all over it. Got some TB cleaner and gave it a nice new shine, and also cleaned out the TB a bit too, mostly the butterfly. Anyways, it seems to have fixed the really bad high idle. But if that naxja thread is any indicator, I shouldn't keep my hopes up to high. These renix's seem to have too many electrical gremlins.

 

I get a slightly high idle on cold starts now, but it will drop down and remain fine after a minute or so.

 

Thanks again! jamminz.gif

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I don't know much but I had random high and real low idle problems. I was trying to get the blowby under control and used some high temp RTV to seal around the forward line in the valve cover that goes to the air box. Well since doing that I have had a much more consistent idle. Maybe coincidence?

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Vacuum leaks will cause problems with idling. Start the engine and spray TB cleaner (some people use water) around the intake manifold and any other gasket (e.g. TB) or vacuum line connection. If the idle drops you’ve found yourself a leak. On one of mine the intake manifold was the problem around the #5 & #6 cylinders. I just re-torqued the nuts and it’s been fine ever since.

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Vacuum leaks will cause problems with idling. Start the engine and spray TB cleaner (some people use water) around the intake manifold and any other gasket (e.g. TB) or vacuum line connection. If the idle drops you’ve found yourself a leak. On one of mine the intake manifold was the problem around the #5 & #6 cylinders. I just re-torqued the nuts and it’s been fine ever since.

 

Normally you use an unlit propane torch to locate vac leaks and listen for the increase in idle.

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