1988 Jeep Cherokee Clarification on High Idle Problem - Any

1988 JEEP CHEROKEE
193,000 MILES • 6 CYL • 4WD • AUTOMATIC
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GTHOPKINSON
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In warmer weather my Jeep periodically "sticks" at max RPMs upon starting. Can be Corrected by disconnecting/re-connectiing the wire harness from the Stepper Motor while engine is running. Upon re-connecting harness idle returns to normal.

Actions taken:
Stepper Motor replaced twice
All throttle linkages checked ok
TPS sensor replaced and factory set

My questions are:
"What sensor(s) would cause the stepper motor to max out the idle after starting?"
"What sensor(s) affect the stepper motor's potion in general?"
"What component(s) relay air temperature information to the engine during start up?"

Any suggestions are more than appreciated!
Mar 7, 2010 at 5:45 PM
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RACEFAN966
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I would check the coolant temp sensor under the intake near the left engine mount. Ohm is when it is cold and get to me with the ohms and the air temp at the time.
Mar 8, 2010 at 9:26 AM
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GTHOPKINSON
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Went ahead and tested the MAT sensor too.

Tested at 20k ohm setting, engine cold

Temperature Coolant Sensor; 5.78 @ 52* fahrenheit
MAT Sensor; 5.76 @ 52* Fahrenheit
Mar 8, 2010 at 8:12 PM
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RACEFAN966
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Ok with the ohms you gave at the temp it is not acting up at the moment as it tests correctly. But the coolant temp sensor is responsible for engine warm up engine speed. So this is why I think you should replace it. If you are having fuel consumption problems it will help that too.
Mar 9, 2010 at 8:43 AM
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GTHOPKINSON
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My gas mileage hasn't been all that great last year or so, but I have just chalked it up to an old engine (almost 200k miles on it). I will change the coolant sensor out and let you know the results. Thank you for the help!
Mar 9, 2010 at 9:28 AM
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RACEFAN966
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Ok sounds good let me know how it goes and if need be we will dig deeper.
Mar 9, 2010 at 9:43 AM