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high idle at start up?

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Old Sep 14, 2010 | 11:03 PM
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mark's91-XJ's Avatar
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From: Norco CA.
Year: 1991 XJ SPORT 2 DR.
Model: Cherokee
Engine: 4.0 600 HP
Default high idle at start up?

1988 4.0L
most of the time it will idle high when i start it, then come down to an idle but uneven rpms, i repleced the icm and cleaned the TB no change. any ideas?
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Old Sep 14, 2010 | 11:11 PM
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Caish's Avatar
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From: Arkansas
Year: 1987 & 1996
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When you cleaned the RB did you make sure the idle speed motor was cleaned up too?
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Old Sep 14, 2010 | 11:15 PM
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mark's91-XJ's Avatar
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From: Norco CA.
Year: 1991 XJ SPORT 2 DR.
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Engine: 4.0 600 HP
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i replaced the ism no change help
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Old Sep 14, 2010 | 11:20 PM
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Caish's Avatar
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From: Arkansas
Year: 1987 & 1996
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Originally Posted by mark's91-XJ
i replaced the ism no change help
Ok might be a vacuum leak, use some starting fluid and start spraying around the intake and the vacuum lines looking for a change in engine sound. You can use brake cleaner, or carb cleaner too.
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Old Sep 14, 2010 | 11:24 PM
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From: Norco CA.
Year: 1991 XJ SPORT 2 DR.
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Engine: 4.0 600 HP
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i did that and i didnt notice any change , all the lines seem to be in good condition, but im with you on that one i just cant find the leak, how much of a change would the motor make?
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Old Sep 14, 2010 | 11:30 PM
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From: Arkansas
Year: 1987 & 1996
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Originally Posted by mark's91-XJ
i did that and i didnt notice any change , all the lines seem to be in good condition, but im with you on that one i just cant find the leak, how much of a change would the motor make?
If there is a leak the fluid would slow the leak down and it should settle into a normal idle till the fluid evaps. One thing I would try, is pull the throttle body off again, and use grease on the gasket to make sure its got a good seal.

How is the voltages? ISM and throttle Position sensor.
How is the grounds on the right side of the engine?
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Old Sep 14, 2010 | 11:33 PM
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From: Norco CA.
Year: 1991 XJ SPORT 2 DR.
Model: Cherokee
Engine: 4.0 600 HP
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Originally Posted by Caish
If there is a leak the fluid would slow the leak down and it should settle into a normal idle till the fluid evaps. One thing I would try, is pull the throttle body off again, and use grease on the gasket to make sure its got a good seal.

How is the voltages? ISM and throttle Position sensor.
How is the grounds on the right side of the engine?
i havent checked but i will when its light, anything else ?
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