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Old 11-13-2015, 01:50 PM
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Shuddering on idle

I have a 97 Jeep Wrangler TJ with 2.5l 5 speed. When I'm in neutral either slowing down or sitting still my jeep will idle low down to like 400-500 rpm and shudder and then eventually stall. It's fine if I downshift when slowing down but I have to constantly give it some gas while idling. I consider myself moderately knowledgable about engines but I have no idea what is causing this. Any ideas?

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Old 11-13-2015, 02:03 PM   #2
Knows a couple things...

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Your IAC (idle air control) is probably dirty and not flowing enough air. Its job is to provide all of the engine's air when your foot is off the gas pedal.

Mounted to the side of the throttle body, you can probably get it cleaned up well enough with an aerosol can of throttle body cleaner sprayed into the throttle body while the engine is running. The IAC will only suck the cleaner through itself when the engine is at idle so you'll have to keep the RPMs as close to idle as possible while spraying it. The engine will die repeatedly during the cleaning when the IAC gets filled up with cleaner at idle RPMs, that's ok, just start the engine again.

There are other potential things that might cause this symptom besides a dirty IAC but those are rare and few between compared to how often/easily the IAC gets dirty. The next most common cause of a bad idle is a low battery, have you had to jump start your engine lately?

Here's where the IAC (Idle Air Control Motor) is located. Notice the Idle Air Control Passage Inlet on the drawing. That is the air intake for the IAC so you'll want to make sure to direct the cleaner's spray at that port when cleaning it.
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Old 11-14-2015, 05:40 PM   #3
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Jerry hit it right on the head. The IAC is most likely the problem. Clean out the throttle body too just in case.

My Jeep sometimes likes to drop to a low idle but it never stalls. I also have bad o2 sensors and they screw up the air/fuel mixture real bad. Sometimes I have to shut off the Jeep and start it back up again so it'll idle correctly
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Old 11-14-2015, 07:21 PM
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Thanks Jerry! That sounds right. I'll check it out tomorrow. I'll let yall know how it works!
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