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Help with engine idle / performance problem

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Ever since I had my MJ (almost a year, it was VERY neglected before I got it) I've had weird idling / performance problems. I'll try to describe them.


In the summer / fall (normal temps) when I started it up the engine would immediately die after running for a few seconds. I would start it up again and it would then run but idle high at about 1100-1200. When I drove it I would notice occasionally the engine would start to sputter and RPMs would drop to like 0 like it was being choked out, even with the accelerator all the way to the floor. This almost always happened right after I started it up, if I had been driving for a while I don't recall it ever happening (trips greater than 30 minutes). When I would stop for lights or stop signs the engine would act like it was choking out and drop RPMs and I would have to press down on the accelerator to keep the RPMs up to keep it from dying (not every time though it was very intermittent and only seemed to happen right after I started driving it). It has cut out on me before and it would start right back up and then be pretty normal (except for high idle around 1100).


Now that it's winter the weirdest thing happened. I hadn't started it in about a month and went outside thinking I will have to start it a few times before the engine wouldn't quit. But to my surprise it started right up and idled normally at around 400 (probably a bit low?) and DIDN'T cut out. BUT once I drove it and warmed the engine up to operating temp, when I would come to a stop the same exact thing would happen, it would sputter and RPMs drop and almost die (would have to keep my foot on the gas to keep it from choking). Once I park it and keep my foot on the gas to get the RPMs up after 10-15 seconds it would idle at 1100 again and be fine.


I have replaced all vacuum lines, cleaned the IAC, checked for vacuum leaks, cleaned fuel tank and intake with seafoam, and replaced fuel filter. I'm thinking this might be a fuel delivery problem since the truck sat for almost 2 years before I got it, I'm sure there's a bunch of crap in the tank maybe plugging up the lines? Fuel pump? I don't know anyone who has a fuel pressure gauge to check to see if it's getting fuel and don't really want to spend $40 just to use one time.


Any ideas or help would be great. Thanks.


88MJ, 4.0L, peugot manual tranny, stock engine parts, 4WD

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The first thing I would check would be the MAP sensor on the firewall. Make sure the vacuum line to the TB is properly connected. I've had this hose come loose, causing the exact symptoms you describe. It's pretty easy to knock loose without realizing it.


Also, if the battery died when it was parked, that could also explain why it started right up after sitting. Basically this would have reset the ECU, and it would run in "limp mode" (straight off the ECU without reading sensor input) until it warmed up and read all the sensors.

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