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Unread 01-12-2014, 02:14 PM   #1
alyman85
Registered User
1985 FSJ Wagoneer 
 
Join Date: Mar 2009
Location: Lansing, Michigan
Posts: 92
IAC issues

I have a 94 4.0, and it has been idleing rough. I replaced the O2 sensor, and replaced the IAC yesterday. The idle shoots to 2200 RPM and will not come back down. I unplugged the battery to reset the computer, and the idle is a little lower, but seems to still climb. When I unplugged the IAC and started it, the idle again rose. I'm guessing the issue is with the IAC but I'm not sure how to fix it. Could it be a bad IAC?

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Unread 01-12-2014, 03:47 PM   #2
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
Posts: 3,893
I seem to remember an aftermarket IAC that was supposed to do that until the vehicle reached 40 mph or so.
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Unread 01-12-2014, 07:22 PM   #3
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,453
did you clean the chamber while the iac was out?
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Unread 01-12-2014, 09:20 PM   #4
JasonStebbins
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1997 ZJ 
 
Join Date: Jan 2009
Posts: 3,138
Did you use an NGK/Mopar oxygen sensor? Just went through something very similar with my wifes Alero. Tried a Denso and it made it worse, AcDelco sensor solved the problem (OEM for General Motors)

As ZeeJay said, clean the chamber the IAC mounts into and clean the throttle body as well.
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Unread 01-13-2014, 09:19 PM   #5
dougmorgan99
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1998 ZJ 
 
Join Date: Nov 2009
Location: Tulsa, Oklahoma
Posts: 194
Cleaned and then replaced my IAC, O2 sensors and TPS trying to track mine down. Finally found it to be my MAP Sensor... Ah well!
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Unread 01-14-2014, 12:30 PM   #6
johns1mj
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1995 ZJ 
 
Join Date: Aug 2013
Location: midland, michigan
Posts: 166
I had a bad connection at the computer. The IAC would test good. The wires would test fine. I had to reset the pin in the connector at the computer.
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Unread 01-16-2014, 10:45 AM   #7
alyman85
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1985 FSJ Wagoneer 
 
Join Date: Mar 2009
Location: Lansing, Michigan
Posts: 92
So by resetting the computer, driving a little bit, and pausing with the ignition on before starting I got the idle to come down to 900-1000.

Except for when it is cold starting. It won't go at all, I have to give it gas. Once it warms up the idle is decent. Never had problems starting with the old IAC, so I'm guessing I have a bad one? Should I replace the TPS too? And if I clean the throttle body does it have to be re-pressurized?
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