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Unread 09-05-2009, 05:05 PM   #1
AndrewMuadDib
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High idle 2k rpm, idle jumping on braking - Moab in jeopardy

I'm going back to the middle east for a fifth year soon and have one window to take my brother up to Moab - and I have to leave in 2 days.

The Jeep started doing two crazy things - 1: high idle any time it's shifted into neutral (exactly at 2000 rpm) and 2: in the past 10 miles it's started high idling then immediately jumping from 2000 to 1000 rpm and cycling back up to 2000 rpm to repeat again - this occurs between shifts and especially when I brake.

I've put six months straight into building for this trip - and I have to find a way to make it work - this is what's in her:

hesco 4.5 l stroker (I-6) 3 years old and 5,000 miles
nv4500
stak mini monster 3
spidertrax 609's, tru-hi 9 and arb's
hydroboost, psc steering
5.5 RK x-factor, 37's

Please help. I need it desperately.

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Unread 09-05-2009, 05:10 PM   #2
Jerry Bransford
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High rpms are generally always caused by a vacuum leak. Something you've worked on that uses vacuum like your hydroboost would be high on my list of things to check. The intake manifold is probably the most common source of vacuum leaks from not being positioned properly while being reinstalled. Head leak?

I'd start looking for a vacuum leak if it were me. Good luck and keep your head down when you get back overseas... from an old vet to you, thanks for your service!
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Unread 09-05-2009, 06:03 PM   #3
tangofox007
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Quote:
Originally Posted by AndrewMuadDib View Post
The Jeep started doing two crazy things - 1: high idle any time it's shifted into neutral (exactly at 2000 rpm) and 2: in the past 10 miles it's started high idling then immediately jumping from 2000 to 1000 rpm and cycling back up to 2000 rpm to repeat again - this occurs between shifts and especially when I brake.
That could be a TPS problem. In normal operation, the PCM fully opens the IAC once the throttle opens beyond a certain point. The high idle condition occurs when the TPS fails to properly communicate the closed throttle condition back the the PCM. For starters, you might try resetting the TPS connector. Disconnecting the TPS during a high idle episode might also be enlightening.
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Unread 09-05-2009, 06:04 PM   #4
Stu Olson
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I the JU forum, I recommended you check the IAC.
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Unread 09-05-2009, 07:49 PM   #5
jmasin
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I'm with Jerry. Since it changes when you step on the brake that really sounds like a vacuum issue to me. The only direct impact the brakes have on the engine running is vacuum due to the booster.
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Unread 09-06-2009, 03:00 AM   #6
Jonny Jeep
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They are the exact same symptoms I had when my TPS went bad. It didn't bring on the check engine light but I did get a code for the TPS show up when I used the key to check codes.
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Unread 09-06-2009, 09:02 AM   #7
jgorm
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I'm with jerry on the vac leak. The extra air has to come from somewhere. Sure maybe the TPS could signal the IAC that there is some throttle position and to open the IAC to the max, but 2000 rpms still seems a bit high to me for that. It may be possible, but its gotta be near the upper limit. I would plug a $10 vac gauge into the manifold and see what it reads. If you messed with the TB stop screw that could cause this also.
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Unread 09-06-2009, 09:34 AM   #8
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Sure maybe the TPS could signal the IAC that there is some throttle position and to open the IAC to the max, but 2000 rpms still seems a bit high to me for that. It may be possible, but its gotta be near the upper limit.
In my experience with that very issue, the upper rpm limit of IAC control is around 3000 rpm when in neutral. In "Drive" my Jeep would do 45 mph on level ground with no pressure on the accelerator.
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Unread 09-06-2009, 10:09 AM   #9
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Well then i stand corrected. Was your IAC sticking open?
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Unread 09-06-2009, 10:19 AM   #10
tangofox007
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Well then i stand corrected. Was your IAC sticking open?
No, it was being "commanded" to open by the PCM. .
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