My 89 will start normal for a while, then all of a sudden, will take a spell and run up to maybe 2k on starting. Ok, I cleaned the IAC, a while back and this fixed it for a while. Now it is doing it again, so I took the pos cable off the batt. then grounded it, and put it back on. It started and ran right, and will do that for a few starts, then goes back to the 2k rpm range, till I ground out the pos. cable again, then it will do right for a few times. Is it the IAC, or something else. Yes this is a 4.0, automatic. Any help will sure be appreciated.

 

I had the same issue with mine, and all I did was get some carb and choke cleaner spray and cleaned out the throttle body. Mine had a lot of sut in it and it was catching on the butterfly.

 

Seafoam.

 

i had the sam exact problem. did you check/ clean the ground wires? this was the single most common problem ive heard about on these older jeeps. i took all mine off, cleande them up with some sand paper or just replaced them all together with heavier wire, i used 2 guage, but 4 will be ok too i believe. sounds like and electrcal problem not a manifold gasket leak but you could always try slowly moving an unlight propane torch around the manifold and vacuum lines just to see if theres a leak. also did you check the iac? could be getting stuck or have a bad wire or something. hope any of this helps or atleast gives you a direction to follow. good luck

 

Confused... whats an iac?

 

I would do a combination of these suggestions. Clean your throttle body out very thoroughly. If cleanning the IAS module fixed the problem for a while, it would indicate to me that it might be the problem. They are fairly inexpensive at advance. Put a new one on there and try it. If it doesn't fix the problem, put it back in the box and take it back... Don't tell them you installed it.

 

Some ppl call it the AIS module. Air Idle Speed. It is sort of like the choke on the throttle body, but not. It opens and closes to allow more air to be pulled into the throttle body during idle.

 

ohh ok thanks