idle issue .. at cold start up .. any advice - thanx in advance - JeepForum.com

 
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post #1 of 6 Old 07-26-2006, 02:01 PM Thread Starter
sanboy
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idle issue .. at cold start up .. any advice - thanx in advance

never happened before ...

drove about 1800 miles on a trip ... got here no problems ..

now every once and while in the morning .. ONLY morning start up
( SEEMS TO HAPPEN 1 TIME IN EVERY 7 DAYS OR SO )

the vehicle will surge all the way to 2000 rpm . then back to 1000 then up to 2000 rpm . then finnally settle in at around 700 or so .....

onec the vehicle is started and it settles down and is driven never happens again that day ..

WHAT SHOULD I BE LOOKING FOR .. ?

any ideas ... ?

thanx in advance for the help


2001 JEEP Grand Cherokee Limited
4.7 - 4x4
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post #2 of 6 Old 07-26-2006, 02:37 PM
greasefingers
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In the Throttle body the butterfly is completely closed at idle. Above and below the butterfly is a channel or bypass. This bypass is the only way for air to enter the manifold, during idle. The butterfly or throttle plate only opens when you touch the gas pedal. In this channel/bypass is a plunger for controlling the airflow rate. A motor moves the plunger in & out. This plunger/motor combo is the Idle Air Control Motor (IAC). Air for start-up and idling is controlled by the PCM. It tells the IAC how much to open/close to let air into the intake manifold.

Symptoms of a bad IAC: hunting behavior of the rpms, extremely high or low idle speeds.

Therefore your problem is most likely one of two things: a dirty or frigged IAC or a faulty TPS throttle position sensor. I would suggest spraying the hell out of the throttle body with electrical cleaner and spray up into the IAC passage.

Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new

Last edited by greasefingers; 07-26-2006 at 08:03 PM.
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post #3 of 6 Old 07-26-2006, 07:52 PM Thread Starter
sanboy
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thanx .. will look into that first thing tommorrow morning

2001 JEEP Grand Cherokee Limited
4.7 - 4x4
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post #4 of 6 Old 07-26-2006, 09:18 PM
zaq123
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Quote:
Originally Posted by greasefingers

Therefore your problem is most likely one of two things: a dirty or frigged IAC or a faulty TPS throttle position sensor. I would suggest spraying the hell out of the throttle body with electrical cleaner and spray up into the IAC passage.

99% IAC. My WJ had that problem. Take it out of TB and you'll see how much carbon got stuck to IAC valve.
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post #5 of 6 Old 08-11-2006, 12:33 AM Thread Starter
sanboy
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spraying it down with MOPAR COMBUSTION CHAMBER spray would work ?

2001 JEEP Grand Cherokee Limited
4.7 - 4x4
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post #6 of 6 Old 08-13-2006, 04:57 PM
mtcox
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I went through this same thing with my 2001 Grand Cherokee. Cleaned the throttle body, didn't work. It was the TPS. I replaced it but apparently I didn't position it properly when I put it back in. The result was erratic shifting, no cruise control and a check engine light. It's a $30 part and solved the problem but be sure it's positioned correctly.
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