Hey, I have a 1998 Jeep Grand Cherokee Limited 5.2 and I've been having some issues with it. It has a high idle issue. When I come to a complete stop it's almost like the motor is revving itself up and I have to put more pressure on the brakes to keep the Jeep from moving but the tachometer only reads about 500-600 rpm's which doesn't make a bit of sense to me. After the Jeep is warmed up and I go to put it in park to shut it off whenever I put it in park it will rev up to about 1200 rpm's then drop down to 800 rpm's and idle there. When at warm idle at a stop light or something of the like it will have a rough, shaky idle. I cleaned the old IAC on it and I've cleaned the throttle body cleaner and that didn't help so I replaced the IAC not long ago and that didn't help either.

Also, this morning on the way to work after the Jeep was warmed up it had a really bad miss whenever I took off from the stoplight. I got it up to about 15mph and it just jerked back violently. It only did it one time but I had to make a turn a few hundred feet after that and when I did the Jeep just shut itself off. It's never done that before. It started right back up and seemed to idle a little better at first but I'm just not sure what caused it to cut off like that. Any help would be GREATLY appreciated!

 

Check the cps and if that is good give it a full tune up plugs wires distributor cap and rotor

 

'98 ZJ's have issues all their own. It's often hard to track down the cause of a problem they might have, so some people keep throwing parts at it until they get it solved.
My advice is to take it to an auto parts store and have them check it to see if it has any trouble codes stored.
X2 on a thorough tune-up with quality parts. It should list the plugs on the core support sticker, or on the bottom of the hood. If not, use Champion RC12LC4 gapped at .040". That's what my V8 ZJ called for.

 

I recommend the accel tune up kit from summit

http://m.summitracing.com/search/Bra...-Tune-Up-Kits/

 

Sounds like a vacuum leak. It's time consuming, but with a vacuum guage go through the whole tree, disconnecting/plugging lines, see what happens to engine vacuum (ie plugging a line that has a leak will increase engine vacuum). Also pull the EGR valve and check that it's not stuck open or has a hole in it. That will cause all sorts of weird idle issues too.

Other things to check, make sure the TPS is in range and make sure there's no mechanical binding of the throttle cable that could cause it to hang.

It's time consuming, but it's free to check out everything first before throwing parts at it. Good luck!

 

His '98 doesn't have EGR. '95 was the last year for the EGR system on the V8 ZJ.

 

I've checked for vacuum leaks etc to no avail. It's still idling high/rough but it hasn't cut off on me again. Although the other day I drove to walmart and came back outside and the Jeep would NOT start. It would crank and crank and crank but would not start almost like it was flooded. I went back in the store and looked around for about 10-15 minutes then came back out and tried it again and again and finally on the 3rd try it started right up. I thought that was really weird.