High Idle problem - JeepForum.com
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post #1 of 7 Old 02-19-2013, 11:57 AM Thread Starter
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1995 ZJ 
Join Date: Feb 2013
Posts: 16
High Idle problem

I recently bought my first ZJ. Got a great deal and spent a whole weekend fixing it. runs great now except for a high idle in neutral or park. It drops down to normal in drive. But in neutral it is like a 1.2k RPMs.

Already checked:
Idle control valve. Clean as a whistle. looks new. cleaned it anyway.

Throttle control valve. was clean already also. no change.

I have been looking for a vacuum leak but cannot find one. All the hoses look great and plugged into the right spots.

Main question:
I noticed that the engine runs a little cold. But not too much. Gage goes half way to middle. whatever temp that is. I figured a lower thermostat was put in. But if this is the case. could the engine be choking and trying to warm the engine up but cant because of a lower thermostat?

any help would be great!!

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post #2 of 7 Old 02-19-2013, 12:52 PM
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1998 ZJ 
Join Date: Sep 2011
Location: Roanoke
Posts: 2,729
If you still suspect a vacuum leak, take some carb cleaner and spray it around the lines. If the engine stalls, or drops in RPM, you've found the leak. Silly question, but is the IAC plugged in all the way? I neglected to push the connector on all the way (I was in a hurry) after I cleaned my IAC and it idled high in neutral and park, but drove normally.

March 2014 GCOTM. 1998 Deep Slate 5.9
On the Jeep:Hot intake, 52mm TB, Summit 8mm wires, catch can, 703s, insulated fuel rails, indexed Champions, Bilstein 4600s, Eibach lowering springs, Moog SS, Ironman mounts, Lotek 2GP, lots of gauges, sparkly paint.
In the garage: M1 4bbl
In the works: Addco/Hellwig sway bars, nitrous, full polly bushings, full exhaust, data logging, billet UD pulleys
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post #3 of 7 Old 02-19-2013, 01:56 PM Thread Starter
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1995 ZJ 
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OK I will check for vacuum leaks again in the morning. Could the IAC just not work even though it looks great? Is there a way to test it without getting a new one?
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post #4 of 7 Old 03-04-2013, 11:46 PM Thread Starter
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1995 ZJ 
Join Date: Feb 2013
Posts: 16
Checked all lines for vacuum leak and found nothing. Looked more into the idle control and saw PO had soldered one wire on it. So I went to the junk yard and cut off a plug. Stripped my wires and soldered new plug on and heat shrinked them nicely. Unfortunately it changed nothing. Idle is still the same. Next thing I can think of is to replace idle control and throttle positioner to see if that makes a difference
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post #5 of 7 Old 03-05-2013, 01:07 AM
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2002 WJ 
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Location: UK
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Try tightening all the intake manifold bolts. It's not impossible that you have a leak around the gasket. That's what caused my high idle.
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post #6 of 7 Old 03-05-2013, 10:45 AM Thread Starter
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1995 ZJ 
Join Date: Feb 2013
Posts: 16
Alright I'll give the manifold a try. Shouldn't the gasket be changed if there is a manifold leak. Just wondering if tightening would help if they are not loose
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post #7 of 7 Old 08-03-2013, 12:57 PM Thread Starter
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1995 ZJ 
Join Date: Feb 2013
Posts: 16
I sprayed all the sensor connection on the TB with electrical cleaner and tightened the manifold. There was definitely lose bolts. I checked the valve covers too and they were all lose as well. Idles like a dream now. Thanks! Late post as well
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high idle , idle , thermostat , vacuum leak

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