I just recently bought an 88' XJ (over paid for all the problems that popped up).
We had a high idle problem and fixed it by replacing the intake. Now we just fixed all the "welds" and did fine for about 2 or 3 starts and the problem is back again.
While in park, it will keep climbing and driving it in this condition, it pretty much drives itself. It might be the throttle cable but then again its a Jeep and its never the simplest of problems. So if anyone can help me figure this out that would be great thanks.
-Chevelle

 

Try This...
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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality

 

yeah...ok. hate to be captain obvious here, but sounds like you still havent fixed your vacuum leak. are you using old vacuum hoses? everything connected properly? you didnt forget to hook anything up? sorry, someone has to ask.

 

throttle cable needs to be checked mine pulled thru the bracket it mounts letting the throttle plate remain wide open suctiopn of motor running held it open ...

 

x2. mine actually was doing this for a while til i replaced the throttle cable.

 

I dont have a bad vacuum leak. Had one before and I know the symptoms they make.

 

Thanks TJWALKER. What you posted seem to have worked (for now) and if the problem persists, I will move to the throttle cable. Thanks everyone for replying
-Chevelle