(newbie)I have an '89 jeep comanche that is driving me insane. (i love my jeep),on cold starts it stumbles and hesitates on acceleration (before shift change) and is now backfiring. My mechanic is stumpted. I had the computer replaced last month (because engine raced on startup and would not return or go to normal idle), 02 sensor 6 month ago (because we thought that was the problem) I have 2098 km's. Does anyone have any idea as to what may be the problem? I live in northern ontario, canada and we do get some pretty cold winter days so I need to get this fixed asap.
Thanks

Oh Suzanna......OK - sorry had to. your Jeep has an adjustable TPS (throttle position sensor) on it. You will need to go to a dealer that has the proper equipment to adjust the TPS in its proper operating range. The tool needed is an early DRB (diagnostic readout box) that allows the user to see if the sensor is in range or not. This sensor is critical as it is directly responsible for air/fuel mixtures and idle quality. Replacing the O2 was a good idea as they had a recall on them way back in the day. The only other item I would look at is tha CPS or crankshaft position sensor. They will cause the ignition to braek up under load. let me know how this works for you!

The Jeeper

Thanks Jeeper, I am going to give this a try. Your solution seems to be the only one so far that makes sense. Prob. won't get to it until after xmas (yikes) but will give you followup. Cheers....S

Good luck and please let me know how you make out! Christmas will be here before we know it. take care-

The Jeeper

Hi, well, decided not to wait until after xmas. brought in the baby and they (dealers)did a diagnostic - TPS, O2 and crank sensors all checked out fine. They could not trace the problem. Now, I should mention the hesitating and backfiring is on cold starts. When the engine is nice and warm it seems to settle down. not disappear completly but close. Can you figure this one out???
Also, don't know if this is important but it seems to me that the whole problem started when I put on a new muffler (necessary). it is not stock. It's a good muffler but belongs on a sports car. Is it possible that this is the culprit??? look forward to hearing back......cheers

I have an '89 Comnche Sport Truck 4X4 2.5L. I love this truck and unfortunately it had an engine fire and is goingto the junk heap. What caught my eye is your mention of the idle racing problem, etc. I experienced the same thing right after re-building the head several years back. I took it to a dealer in the Denver area and they let the engine race wide open for 15 min. while they performed a "computer diagnostic". Their conclusion was to replace the computer as well. I was livid. Any mechanic worth his salt knows you don't idle an engine wide open for more than a few seconds let alone 15min!! MY engine was toast within ten thousand miles. Anyway, it turned out to be loose bolts on the intake/exhaust manifold. They were not seating properly which was messing with the O2 sensor reading. The sensor was telling the 'puter to give it more fuel to balance out the mixture. This may or may not be your problem, but the '89's also had problems (and a recall) with the exhaust manifolds cracking. This could also be the case with your Jeep. If the crack is small enough it could cause you the problems on cold starts until the metal heats up enough to seal the crack. BTW I now own an '88 Comanche I am restoring with the parts from the '89. I hope that helps.

Ruari

Thanks for your comments.....I have since replaced my computer. I sure hope it wasn't just loose bolts,,,aaggh. anyway, the new computer did not address the stumble and hesitation on esc. I fianlly went to a high performance shop and they discovered that my distributor was malfunctioning and the sensor was not sending info to all the cyl so therefore I was running short 1 etc., etc. replaced the distr and holy &**&(, talk about sport truck, it had power that I had no idea I was lacking. she runs like she was new. I sure love her to bits. She has been totally rebuilt and I would hate to put her in retirement. she only has a little over 200,000 klicks and most of them high way and country roads. Again, thanks a bunch for your information. I am going to pass it on to my old mechnanic and keep a reference for myself. cheers