I have a 91 XJ'S with the 4.0 in. I have noticed that some times when I have to really get into the skinny peddle to power up an obstacle or like this past weekend thru some mud then up an incline. When I finish getting out of it it doesn't want to idle for awhile. I have to two foot it for a bit then all returns to normal. Any ideas?

 

My '01 was wanting to die at idle after it warmed up. I replaced the TPS, cleaned the IAC, and cleaned the throttle body. fixed her right up!

 

You may have just gotten water in the intake or in the distributor. Happens all the time its not a big deal as long as it goes back to normal after drying out.

 

Well i thought of that but that and explains when i am in the mud but what about when I am on the rocks and do not hit water?

 

Vacuum? At WOT you have none, then snap to idle....if the ball needs re-charged maybe vac will be low a few seconds. Easy test would be to cap off the large line to the bottle, (rear of the TB on 87-90)...then see if that helps. Maybe not likely, but easy enough to test.

 

Is it the same on the 91? When this happens it won't stay running for awhile. I will check for vac leaks I am sure I have one or two.

 

I bet it has a fair sized, (3/8?) tube coming off the intake somewhere, that goes back to the firewall, across to the pass side, then forward all the way to the vacuum ball behind the RF bumper. Those crack, fall off, the lines can come off. That happens. (then it has a small tube comming back to work the vents and cruse)

Not saying it's likely your issue, but maybe. Something to check anyway.