Idle bounce update
01-01-2017, 07:24 PM
#1
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Model: Cherokee
Idle bounce update
Can't find my last post on this, but as I have stated in the past I have jumping rpms at idle. The rpms constantly move +/- 50 and you can feel it and it annoys me.
I have recently noticed it does not do this when the a/c or defrost is on. The needle is pin straight at about 100 rpms higher. So what does that mean? Is there really no fix for this?
Tps and iac have been recently replaced with no improvement
I have recently noticed it does not do this when the a/c or defrost is on. The needle is pin straight at about 100 rpms higher. So what does that mean? Is there really no fix for this?
Tps and iac have been recently replaced with no improvement
Last edited by Jalebate; 01-01-2017 at 07:27 PM.
01-03-2017, 05:35 AM
#3
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Year: 2001
Model: Cherokee
Engine: 4.0
Annoying idle issue
Can't find my last post on this, but as I have stated in the past I have jumping rpms at idle. The rpms constantly move +/- 50 and you can feel it and it annoys me.
I have recently noticed it does not do this when the a/c or defrost is on. The needle is pin straight at about 100 rpms higher. So what does that mean? Is there really no fix for this?
Tps and iac have been recently replaced with no improvement
I have recently noticed it does not do this when the a/c or defrost is on. The needle is pin straight at about 100 rpms higher. So what does that mean? Is there really no fix for this?
Tps and iac have been recently replaced with no improvement
I have the EXACT same issue and have also cleaned the IAC, throttle body, adjusted the accelerator cable, replaced spark plugs, checked for cracked head/leaking gasket(s), and had a dio done with no recorded issues, ALL to no avail! Still can't figure this thing out and IT IS ANNOYING!
Further advice and more info on fixing this MOST ANNOYING idle issue would be great! ANYONE WITH FIRST HAND EXPERIENCE PLEASE
01-03-2017, 09:01 AM
#4
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Year: 1999
Model: Cherokee
Engine: 4.0
The IAC control system in the PCM is complicated.
The reason you don't see RPM flux when AC or defrost is selected is that the PCM recognizes the AC request and will bump the IAC position to increase the idle RPM. With AC off the PCM returns the IAC control to normal operation.
You may have a defect in the wiring going from the PCM to the IAC or the PCM memory cell is corrupted somehow.
Try clearing the PCM adaptive memory to see if the PCM IAC control memory can be relearned. Doing so will cause strange IAC behavior for awhile until the PCM relearns.
Try this clearing procedure to see if it any effect. If this procedure does not affect the idle RPM problem (eventually) there may be a defect in the PCM. The fact that the RPM gets smooth when AC is selected indicates (to me anyway) that the PCM to IAC wiring is good.
ClearingKeep Alive Memory and Relearning Adaptive Strategy
KeepAlive Memory And Adaptive Strategy:
The Electronic Engine Controls system constantly monitors and adjusts the PCMcalibration to correct for normal wear and aging of components. The PCM usesthese calibration adjustments to shift fuel delivery calculations and idlespeed specifications to compensate for the aging of the vehicle.
When a systemcomponent is replaced, the Keep Alive Memory (KAM) should be cleared to erasethe information stored by the processor from the original component.
ClearingKeep Alive Memory:
To clear the KAM, disconnect the battery negative terminal for five minutes ormore (preferably 15 minutes).
AdaptiveStrategy Relearn Procedure:
After repairs have been made and the KAM cleared drive the vehicle for at leastten miles to allow the PCM to relearn the values for optimum performance.
Note: Duringthe ten mile relearn drive, the vehicle may exhibit some drivability symptoms.These should be eliminated when the KAM has relearned the operating values.
The reason you don't see RPM flux when AC or defrost is selected is that the PCM recognizes the AC request and will bump the IAC position to increase the idle RPM. With AC off the PCM returns the IAC control to normal operation.
You may have a defect in the wiring going from the PCM to the IAC or the PCM memory cell is corrupted somehow.
Try clearing the PCM adaptive memory to see if the PCM IAC control memory can be relearned. Doing so will cause strange IAC behavior for awhile until the PCM relearns.
Try this clearing procedure to see if it any effect. If this procedure does not affect the idle RPM problem (eventually) there may be a defect in the PCM. The fact that the RPM gets smooth when AC is selected indicates (to me anyway) that the PCM to IAC wiring is good.
ClearingKeep Alive Memory and Relearning Adaptive Strategy
KeepAlive Memory And Adaptive Strategy:
The Electronic Engine Controls system constantly monitors and adjusts the PCMcalibration to correct for normal wear and aging of components. The PCM usesthese calibration adjustments to shift fuel delivery calculations and idlespeed specifications to compensate for the aging of the vehicle.
When a systemcomponent is replaced, the Keep Alive Memory (KAM) should be cleared to erasethe information stored by the processor from the original component.
ClearingKeep Alive Memory:
To clear the KAM, disconnect the battery negative terminal for five minutes ormore (preferably 15 minutes).
AdaptiveStrategy Relearn Procedure:
After repairs have been made and the KAM cleared drive the vehicle for at leastten miles to allow the PCM to relearn the values for optimum performance.
Note: Duringthe ten mile relearn drive, the vehicle may exhibit some drivability symptoms.These should be eliminated when the KAM has relearned the operating values.