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Unread 12-16-2005, 04:25 PM   #1
dodgetk81
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1997 TJ Wrangler 
 
Join Date: Mar 2004
Location: PA
Posts: 529
OBD Code P0505

I got a CEL today and my 96 ZJ 4.0 would start but would not idle, Take your foot off the skinny pedal and it just shut off. The light was not on until this happened. After a couple minutes of holding it at 1500 rpm, it ran fine but the light was still on. I got a code po505 it is an idle control system malfunction. I turned the light off and all is well at the moment. Does anyone know what I need to check or replace? Thanks
Don

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97 TJ 4.0, auto, 4.5" RE long arm, 33 " MT/R's on Moabs, 4.10's, 8.8 w/Aussie locker, A to Z rockers, A/A SYE, Warn M8000, Vanco
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Unread 12-16-2005, 06:33 PM   #2
greasefingers
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1994 ZJ 
 
Join Date: Sep 2003
Location: Northern VA, USA, NJ
Posts: 8,237
The PCM has Inputs and Outputs. The Inputs are from sensors like the temperature and the throttle position and the outputs are for controlling actuators like the IAC motor and fuel injectors.

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 valve 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.

Therefore your problem can be only one of two things: a dirty IAC or a faulty PCM. I would suggest spraying the hell out of the throttle body with electrical cleaner. Then since yours is really screwed up, I would remove the IAC for better access and cleaning. Never move the plunger. It can become damaged easily if you slide it in and out. There is no electrical test for diagnosing the IAC that I am aware of. This is one of the cheapest sensors for the jeep $ 32/ea. If this were my problem, I would instantly replace the sensor.
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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
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Unread 12-17-2005, 06:14 AM   #3
dodgetk81
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1997 TJ Wrangler 
 
Join Date: Mar 2004
Location: PA
Posts: 529
I cleaned out the TB when I purchased the Jeep. That was only a month ago. Ill replace the IAC and hopefully thats the answer. I hope its not the pcm. Thanks greasefingers for the helpful and very informational post.
Don
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97 TJ 4.0, auto, 4.5" RE long arm, 33 " MT/R's on Moabs, 4.10's, 8.8 w/Aussie locker, A to Z rockers, A/A SYE, Warn M8000, Vanco
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