I checked for a vacuum leak and there is no leak. I took my air cleaner hose off to clean the throttle body and the IAC off.

It sometimes idles at 1500 in park and 900 in drive even when WARM. If I go for a 1-2 mile drive then it will return to normal idle at 700 in park and 600 in drive.

87 4.0L I6.

 

Mine does the same thing when the A/C coolant is low. If it does it when you not in defrost or A/C then it is not the coolant.

 

my old xj used to do the same thing sometimes, pretty sure it was a tps sensor but i never got around to looking into it before i sold it

 

My 89 xj has the same problem sometimes it likes to go up to 2,000 in drive. It wants to push through stop lights. And I already have bad brakes as is. I will be watching this. I've tried everything. Replaced my iac. Swapped it with the my 88 comanche which runs just fine with the xjs. I have adjusted the tps and done the ground refreshing. I'm about to replace the tps. Can't switch them between the mj and xj cause the mj is a 5 speed.

 

Mine is a 98 so I don't know if it will matter for you, but mine would randomly idle high until I replaced the TPS with a new one. It doesn't do it any more.

 

I belive you have the C101 connector on ghe driverside fire wall. You should take it apart and clean the tar like substace out of it. Also there are factory crimped grounds in the wire loom near the fire wsll and going down the injector rail. Cut out the grounds that are factory wrspped in duct tspe and solder them all together. Your idl issue may go away after that. That wss the problem in my 88.

 

If the TPS doesn't solve it, try looking at the IAC

 

My 88 does have the c101 and my 89 does not. But the 89 likes to high idle. Sorry for any confusion. I also don't mean to take over anyone's thread. I just have a similar problem and would like ways to fix it.