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Old 04-10-2011, 02:09 PM   #1
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Exclamation high rpms when cranking

i have a 2002 jeep tj with 4.0, has 84,000 miles on it. when i crank it up the motor runs up to 2000 rpms, then goes back to normal, mostly when the oil pressure gauge reads up to around 45-60 lbs, which is about 15-45 seconds. it just started doing this about a week ago, so i have tried fuel injection cleaner you add to gas and also cleaned the throttle body out with carb cleaner. any ideas?

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Old 04-10-2011, 05:01 PM   #2
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Quote:
Originally Posted by coachwalt
i have a 2002 jeep tj with 4.0, has 84,000 miles on it. when i crank it up the motor runs up to 2000 rpms, then goes back to normal, mostly when the oil pressure gauge reads up to around 45-60 lbs, which is about 15-45 seconds. it just started doing this about a week ago, so i have tried fuel injection cleaner you add to gas and also cleaned the throttle body out with carb cleaner. any ideas?
U clean the iac valve. It idles high when u start the jeep and then lowers after a few minutes. Maybe it's sticking.

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Old 04-11-2011, 06:36 PM   #3
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kjeeper10, thanks i tried that last night and it did fine, but this morning it revved up to 3000 rpms and the motor made a knocking sound for just a few minutes. this afternoon i drove it home from work and it went up to 2000rpms but settled down after a few moments. any other ideas?
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Old 04-11-2011, 07:41 PM   #4
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Did you disconnect the iac and see if there is a change? I'm no pro but been through a lot with my jeep. usually when something like this happens the check engine light comes on, I'm assuming that's not the case. If it's not a bad iac, check for the more common things that go bad like vacuum leaks or the other sensors like the throttle position sensor. Most of the time these trigger a CEL but you never know. I had a leaking intake manifold making this load whistling sound and no light and nobody could figure the damn thing out, untill I just had it replaced and that fixed my problem..
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Old 04-11-2011, 07:48 PM   #5
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And if you were to rev it to 3000 in neutral it misfires, I think thats normal and maybe what you heard
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Old 04-11-2011, 08:02 PM   #6
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This is a thread I dug up and I had to look closely cause it's almost identical with your ? And my first guess. It elaborates more on the IAC VALVE

http://www.jeepforum.com/forum/f11/e...ranked-961497/
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Old 04-12-2011, 04:02 AM   #7
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sounds like a vacuum leak to me, im no pro but to my knowledge the jeep (and most other cars) dont start reading any input from the sensors/computer untill it has warmed up a bit, then begins to take in readings from the computer,from what ive seen high idle at startup means its a vac. leak and the reason it goes to a normal idle rpm after 45ish seconds is the computer compensating for the leak once the car warms up and starts reading the sensor info

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