My 89 XJ Limited is sporadically idling fast at start up, right around 3,000 rpm. What would cause this? This is an intermittent problem that only happens occasionally.

 

vacuum issue. check lines and *****… lolz.. Awaiting puns..

 

Besides vacuum, the IAC can cause high idle. If just turning it off and restarting changes or fixes it, that would point to the IAC being sticky. I cleaned mine a number of times before I found the plug it's self was the culprit.

 

What is IAC?

 

Idle Air Control. It's on the front right of the TB. (throttle body). You should be able to search it. There might be info in Cruisers tips as well. Actually you would benefit to do 1-5 of his tips first, before anything else.

His link is on-top in the link in my sig, and here> https://www.cherokeeforum.com/f51/cru...x-tips-153657/

 

Probably a bad TPS, but I would do Tips 1,3,4 and 5 before condemning the tPS.

Correct procedure to adjust/diagnose TPS is Tip 8

 

Thanks the IAC was caked with soot plus I did find on the side of the Throttle body the plug on the right side at the rear (dual port 1 with vacuum line 1 plugged) was actually popped out of the throttle body. I cleaned it up and put it all back together and she idles better than she has in 4 yrs that I have owned it.

 

Yes! Partly right :P Glad it's running strong! Have you done any other routine maintenance to the ignition system- cap/rotor, plugs/wires, cleaned grounds?