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Old 07-12-2010, 12:56 PM
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Red face Problem w/ idle on 1999 Jeep Wrangler

I have a 99' Wrangler 6 cyl 4.0 that idles high, about 1200 RPMs when in Park or Neutral... runs fine while in gear, no starting issues, never really run the A/C.

Thought it could be a vacuum leak, found a hose that was disconnected, got it hooked back up but the problem continues. Thinking it might be the idle control valve or fuel filter but I have no issues with stalling or idling low, just a higher idle in park and neutral. Any thoughts?
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Old 07-12-2010, 01:03 PM   #2
Knows a couple things...

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The first thing I would do is to use an aerosol throttle body cleaner to clean the throttle body's interior while the engine runs. What you're really trying to clean is the IAC (idle air controller) that is attached to the side of the throttle body. The IAC gets dirty and when it does, it can stick and cause idle problems. Just make sure some of the spray gets into the IAC's air passage inlet slot you can see in the illustration. It's definitely not caused by a fuel filter problem which wouldn't cause a high idle no matter what.

If it's not a dirty IAC and you are 100% certain there is no vacuum leak, the next most likely source of the problem could be the throttle position sensor which is also attached to the throttle body. Though when it goes bad, it must be replaced.

Has anyone ever worked on the exhaust header or intake manifold? When the intake manifold isn't properly seated against the head, a high idle is the invariable result.

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Old 07-12-2010, 01:32 PM
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Thanks! I'll check it out tonight and see what I can figure out! Much appreciated.
1999 Jeep Wrangler
4.0 6 cyl, hard top
Yakima, WA
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issues engine idle

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