I have a 89 xj I just bought. It needs alot of work the guy I bought it from did some wierd stuff anyway my idle will sometimes go up to 2700-3000 rpms when I fist start it up and wont come down until I shut it off then it will idle at around 1500 rpms and then sometimes around 900 (nomal I think) what should i look at?

 

my 87 did the same thing when I first got it home.I went through and checked all my conections first it ended up being my idle position sensor motor. Its bolted right in the throttle body under the air intake boot.

 

Check all your vaccum lines, might have a leak some where.

Also, not too familiar with jeeps to be honest, but if yours is Fuel Injected and not Carburated (sp?), check you IAC (Idle Air Control) Valve, it might be old and gummed up.

 

Try adjusting your tps. Its mounted to the throttle body. Pull it off and turn the rod in it .

 

+1 on the TPS and checking for vac leaks. Mine did the same thing ... TPS was the 'bad dog'