I have 89 with the 4.0. Today I was driving and the jeep just died, and wouldn't start back up. A little while later I got it to start, but the rpms were all over the place. It would run fine for a minute, then it would try to sputter out and die. If I kept the rpms over 2k it would stay running, but they would would dip and sputter until it eventually would just die. I can't find any physical evidence as to why, and there was no prior symptoms that might point me in the right direction. Everything was running fine until it died. Can anyone help me out. I'm at a loss at the moment.

 

I feel your pain. I have a '89 also, the wiring is old. I'd start there. My 88 MJ had a similar idle problem. I'd tap the TPS & it would go away. My 98 XJ would die after 45 minutes of driving. That turned out to be the CPS.
Good luck.

 

Go to www.cruiser54.com and perform Tips 1,3,4, and 5 and see what that does for you.