sworddylan

Hello all, Im working on my neighbors 89 Comanche. Its an auto, 4.0L. The issue im having are, long starts for what thats worth, main issues are it seems to be idling high in park, no tach so cant be sure on the rpm and itll occasionally rev up a few hundred rpm for a bit and then go back down. Sometimes, seems more when its cold, itll suddenly idle lower and then back up. The other issue its having is, it will stall while hes towing his horse trailer. Regular driving seems to drive alright, never tried to stall on me while i drove it, once while slowing down to an almost stop it felt like it idled down low but didnt die. Ive checked everything i can think of, Idle air valve is clean, i replaced it to see if it help and it didnt seem to. Tps tests out fine and was a bit out of adjustment, reset didnt seem to help. Coolant temp sensor checked out, intake air temp checked out, the cage was melted but the readings still seemed good. Map sensor seemed to be working, readings were low, but i attribute that to the high idle, when it revved up it dropped further. Egr also seemed fine, wasnt stuck open. I disabled it to eliminate it as a possible issue. I also cleaned the throttle body. Checking over a few other things, the timing does not flecuate when it revs up and down. the iacv does not seem to move when it revs up and down, verified by spraying some brake clean in the little port and when it revved up it did not suck the brake clean in. Im suspecting the o2 sensor, as i feel ive narrowed it down to the ecu adding or pulling fuel ultimately causing it to rev up and down. I would think the o2 would be the likely cause. Hoping someone who is better with these jeeps can chime in.

cruiser54

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