Engine not running smoothly after start up

RICKBMI

MEMBER
1998 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
100,000 MILES

Hello gentlemen,
I am not sure how to explain this problem.
I suspect that it started after I checked the air filter few months ago. The symptoms are a bit weird: After starting the engine, without problems, the engine runs well for a while, and then it starts to run erratically and to shake like it would choke. It does that for a while when I warming it up, and then, out of the sudden runs well and this is it. If it happen to drive right away, it does the some thing and I am loosing power on gas, looks like is stopping, does the choke thing few times, and the again, starts to run well. This is happening regardless of the engine temperature, or maybe not. If I stop for two minutes, and start again, the thing does not happen, but if stays longer eg 5 minutes, it is happening again. The engine check light is not on. After choking, the engine runs perfect, no hesitation, I could drive 90-miles/h, without problems. Sometimes is not doing the thing for a few days, and then it does again. It happened once when I put Shell instead of Chevron, but when I put Shell again, did not work.
I changed sparkplugs, rotor cap, cables, air filter, most mechanics have no clue, and asked to leave the car with them for two days, not possible at this time.
Any hints please?

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

It sounds like you could have an issue with the idle air control valve.
When the IAC valve gets dirty it can have intermittent impact on the idle quality.
The IAC will become dirty over time due to heavy air particles attaching to the valve. A condition called coking.
The IAC is located on the throttle body.
You might able to clean out the IAC, this can improve the drivability issue that you are experiencing.

Here are couple of helpful articles:

https://www.2carpros.com/articles/how-a-idle-air-control-valve-works
https://www.2carpros.com/articles/idle-air-control-valve-service

It will also be a good idea to clean out the throttle body as well.

I have attached the diagrams for your reference.

Please let me know of any questions.

Thank you.

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