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Old 03-01-2011, 04:42 PM   #1
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Idle High, IACV Reset?

I come to the great collective as a confused man. I have a '92 with the 4.0L engine. Engine cold, engine warm, it doesn't matter. When I start up, the engine idles fine. By the time I've driven 3 miles, at varying speeds, the idle is up to 1800-2000. If I shut down the engine for 15 minutes and then restart, it idles at 650-800 just like it should. Until I drive a couple of miles, and it goes back up. If I run down the highway at 65 for awhile, the idle is above 2000, close to 2500, and stays there until the engine is shut down for that same 15 minutes. I changed the idle air control, and actually read and followed the enclosed directions for installation, but the problem persist.

Is there some secret reset button I don't know about?

Anybody got a suggestion where to go next?

TIA,
Tom

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Old 03-01-2011, 05:34 PM   #2
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Working on the exact same problem on a '92 Renegade 4.0L
Changed both the IAC and the TPS today with no luck. Vacuum lines all good.
Had to jump start it this morning so the ECU may be confused. Going to unplug the battery overnight and see if that fixes it.
I'll keep you posted if I find a fix.

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Old 03-01-2011, 09:38 PM   #3
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We are in sync. My battery is disconnected for the evening as well. I hope it works for us.

Tom
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Old 03-02-2011, 11:58 AM   #4
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I hope disconnecting the battery worked for you. It didn't for me!
Tom
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Old 03-02-2011, 12:51 PM   #5
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Fixed!
Turned out I had a few loose bolts on both the intake and exhaust manifolds. Just enough to screw up vacuum. Torqued them down and the problem vanished instantly.
Here are the bolt torque specs from the book:
23 foot pounds - Intake
23 foot pounds - Exhaust outer bolts
30 foot pounds - Exhaust inner bolts
You need to check them all above and below. Even the ones that are damn near impossible to reach.
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Old 03-02-2011, 05:36 PM   #6
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Thanks! I'll do that this weekend.
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Old 03-03-2011, 12:03 PM   #7
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You, Sir, are a frigging genius!

I checked the intake bolts and found several loose. Tightening them fixed the problem. I owe you one.

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