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Unread 08-22-2009, 08:03 AM   #1
RamboPants
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Random High Idle when A/C is on?

My jeep has i had a high idle problem for about a year or 2 now so im sure its all coming from the same place I just can't pin point it. The High Idle upon start up that won't stop unless i turn the jeep off of like 20 seconds and the High Idle at random when the AC is on... Starting to think is electrical anyone have any Ideas?

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Unread 08-22-2009, 08:21 AM   #2
tjwalker
It's the crank sensor!
 
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Best place to start with an idle problem is by removing and cleaning the idle air control. They get carboned up over miles and time.

The IAC is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE IAC

1. Remove the IAC with a torx driver (2 bolts, one may be kind of hard to get to)
2. Gently wiggle out the IAC from the throttle body
3. Clean the IAC with throttle body cleaner. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, won't harm the coatings on throttle bodies and is formulated specifically for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle as it is fragile and you could damage it.
4. Also thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner
5. Consider cleaning the entire throttle body itself and all associated linkage as long as you’re at it
6. Reinstall IAC and check idle quality
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Unread 08-22-2009, 10:37 AM   #3
RamboPants
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Yeah i have already replaced it 3 times over the years its not the IAC.
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Unread 08-22-2009, 04:49 PM   #4
mark02tj
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Would a dirty/defective IAC also cause this problem... My daughter's new to her 1990 XJ idles up and down when it's cold. By this I mean it will spike up to about 1200 RPMs and then drop to 300 RPM or so. It's up and down and up and down and up and down.... for about 3 or 4 minutes until it's warmed up a bit.

BTW, she has the 4.0L, automatic.

SORRY for hijacking the thread!!
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Unread 08-23-2009, 09:09 AM   #5
RamboPants
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Yeah, Now that i would try cleaning first and check for vac leaks.
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Unread 07-20-2012, 11:18 AM   #6
TimboTJ
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Did you ever solve this?

Mine does the exact same thing. Idles around 1000 rpm, then revs up to about 1200 when the a/c clutch engages, then back down to 1000 when the clutch disengages. Also, very fast idle after start. I've already replaced the TPS, about a year ago, it threw a code. I've cleaned the throttle body and replaced the IAC motor, but it still does the same thing.

The fact that it revs as the a/c kicks on and off tells me that the IAC is indeed working, it's supposed to add a slight amount of power to counter the draw from the a/c compressor, just not this much. Thinking it's something electrical.

Not sure where to look next.
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Unread 07-29-2012, 08:45 PM   #7
RamboPants
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not really It still comes and goes.....
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Unread 07-30-2012, 07:19 AM   #8
TimboTJ
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Same, mine also comes and goes. It seems better if I start it with the A/C off. Not sure where to start looking.
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Unread 07-30-2012, 12:08 PM   #9
440_Magnum
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Add my 2001 to the list- it does the same thing. No rhyme or reason to it, and I've cleaned the IAC valve, checked for vacuum leaks, etc. Besides, it idles normally if you turn the AC off so those things can't be the problem. Its almost like the software is programmed to bump the idle up TOO much to compensate for the AC. The 99 doesn't do this at all.
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Unread 07-30-2012, 12:14 PM   #10
TimboTJ
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Mine idled just fine for the first 80,000 miles, so it used to work fine (now has 91,000 miles).

I keep thinking it has to be an electrical problem somewhere.....as it sometimes idles just fine, right around 700 rpm, and stays there even with the a/c switching on and off.

Did a full computer reset, cleared the adaptive memory last week....still does the same thing. Not throwing a code either.

'02 4.0 liter Sport, 5 spd.
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Unread 02-11-2013, 08:56 AM   #11
TimboTJ
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Anyone?

Still have the same problem, but not as much in the winter. No codes.
Thinking about changing an O2 sensor, maybe a temp sensor somewhere?
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Unread 08-12-2013, 07:54 AM   #12
TimboTJ
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Frustrating.... The problem seems to be worse in the summer when the engine is hot. Still trying to figure it out.

Anyone.... Bueller.....Bueller ? ?
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Unread 08-12-2013, 09:23 AM   #13
RamboPants
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Yeah I had to do some re wiring to the harness beside the air cleaner, I eventually replaced the harness a few months back. I have been checking and testing wires for the last few weeks when i have time because I'm now having low voltage problems when the A/C is on .
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Unread 08-12-2013, 09:47 AM   #14
TimboTJ
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So you're still having a weird idle problem ?
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Unread 08-12-2013, 02:39 PM   #15
TimboTJ
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Update

Just got back from the shop, they did a factory reset of the PCM and it idles perfectly now...... so far.
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