idling problems after warmed up

[Jclow87]

Hello all!

I have a 1992 Cherokee 4.0 and I'm having some problems with it. It is having issues at idle trying to move from a stop. I usually can drive it to and from work, but after work driving it seems to almost choke out when i come to a slow or stop. It does it overtime i try to move it in drive or reverse from a parked position. It sounds like its almost choking out, i have to keep pumping the gas pedal and eventually, after a lot of backfires, it will rev up and seem to almost "clear" whatever is wrong and then it will drive fine. I recently replaced the MAP sensor and TPS sensor, as well as the fuel pump ballast resistor. No check engine light on. i did notice my exhaust is leaking in front of the muffler, but just a small hole. i am also in need of a rear main seal job. though i figured these weren't the issue. is this a fuel pump/filter issue? or electrical? i live in south lake tahoe, and we are covered in snow, so i figured to ask the experts before I'm crawling around in the snow trying to figure it out. thank you in advance for the help!
-jordan

[8Mud]

A CPS covered in oil can cause issues, mine was a rear valve cover leak. I cleaned mine off with brake cleaner (what the heck worth a try) and it worked fine. Oil covered CPS usually causes hard starts. but may sporadically sputter, backfire, stall and fail to idle. Not sure if cleaning it with brake cleaner is a fix, but it worked for me (that was like three years ago).

A O2 sensor on the way out will also cause this, usually only happens after a minute or two of warm up after the motor switches to open loop. Mine would run fine for about 3 minutes maybe, then things would get iffy from there. Also seemed really sporadic, sometimes it would act up, other times not so much. Never did throw an O2 code, which led me to believe the O2 sensor needs to be really bad before it pops a code. I first replaced the TPS (no help), then replaced the front O2 sensor on a hunch that cured it.

IAC can be cold weather and low voltage sensitive. The gunk in the IAC gets stiff in cold weather. Usually gets better after the motor warms up.

The IAC needs a good battery and charging system to work well. Numerous times the first sign I need an alternator or a battery was IAC issues.

If nothing else works out for you, park it in a heated garage overnight, put a can of gas tank defroster in and see what happens. Not real uncommon for the fuel to get a lot of moisture in it, either from the gas station tanks or because of condensation in the fuel tank. I once pulled a heaping handful of ice out of my fuel tank, made me a believer.