Cleaning IAC & Throtle Body?

What is the best way to clean the IAC and the throtle body on a 4.0?
Still trying to cure a high idle when warm and no idle when cold?:dunno:

Throttle body cleaner. Intake cleaner. Where in Oregon are you? My dealership would also, in extreme cases, pull the throttle body and solvent tank it. Hope that helps.

Use throttle body cleaner for the throttle body, brake cleaner for the IAC.....then shoot a squirt or two of WD40 down inside the shaft where the spring is for the IAC. Not too much!

Clean with the engine off first, use a rag and old toothbrush (well I guess you could use a new one if you want, but it won't taste too good when you brush your teeth). Wet it down and wipe away with the rag and use the toothbrush in the nooks & crannies, open the butterfly valve all the way by hand at the throttle lever and repeat with rag and tooth brush.

Then run the motor and spray the solvents in there. Be ready to bip the throttle lever by hand to prevent stalling the motor out. It will really want to do it as you spray the cleaner down the IAC port.

Have you checked fault codes from the PCM? I think the '89 was capable of the CEL blinking out the fault codes.

1989cherokee said:

What is the best way to clean the IAC and the throtle body on a 4.0?
Still trying to cure a high idle when warm and no idle when cold?:dunno:

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With an O2 sensor downstream I'd be careful about what you spray into and burn through the engine. Also, don't spray anything into the TPS.

I prefer to take my TB off and it never needs to be dipped and if careful can reuse gasket, cheap - stock spares. Just remove the IAC, clean all that good and spray/wipe out the main bore. Again, just try to leave the TPS alone for now until you qualify the IAC circuit and get it working. It doesn't sound to me that it is if it doesn't idle cold.

You can also remove IAC from TB, leave wiring connected and cycle ignition on/off watching to see if it moves. After every shutdown, it should pull-in to simulate slightly open throttle position for restart.

It's a funky circuit and you need to download/read FSM to better understand how to best adjust everything and qualify the components. Even still, the IAC screws-up on these Renix models and nobody really knows for sure why. I finally built an IAC tester (bi-polar stepper motor controller) and now use it to adjust my idle with a pot to whatever I want for my situation.

Yes, it needs to be cleaned and IMO it's best to take-off from the vehicle to prevent something from running through engine and O2 that doesn't need to.

Lagrande, Oregon Thanks for all of the advise! Bought this one new so i plan on keeping it, 218k runs great just not below about 35 mph with your foot off the gas. Have tryed all the usual things to correct high idle, but whats the deal with no high idle when cold? and when i turn on the AC it does not idle up like it use to?

1989cherokee said:

Lagrande, Oregon Thanks for all of the advise! Bought this one new so i plan on keeping it, 218k runs great just not below about 35 mph with your foot off the gas. Have tryed all the usual things to correct high idle, but whats the deal with no high idle when cold? and when i turn on the AC it does not idle up like it use to?

Click to expand...

IAC circuit ain't working. AC should kick it up too. Pull a small vac hose and it will go up a few RPM and stay there. If IAC were working, it would settle back down after introducing a small vac leak. Like I said pull it out and watch it on/off ignition. 99% sure it ain't moving. Why? When was the last time it was replaced? You can OHM check the bi-polar stepper motor if you understand what it is. Google is your friend.

You need to read a factory EFI manual and understand Renix. Keep asking questions, some folks know it quite well and can help if you put in the time to understand the components and what is expected of each system at each point in the operating range.