kais3r
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- Mar 19, 2014
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- VX Executive S2
Hi, I've been trying to sort this issue for a while but am not sure what to try next.
The engine will rev higher than normal when cold, usually in the range of 1200-1700, typically at 1500 approx, this goes away once the engine comes to temperature or has been turned on and off a few times before driving (takes a fair few tries and a couple mins to settle), during the time the problem exists the revs will fluctuate at times jumping by a couple hundred (usually upwards) also pushing the throttle does at times make the revs sit higher than they were before, though not as high as I pushed them, eg. 1500, rev to 2500, drops back to 1700.
Throttle cable and associated parts are all ok, this seems to be isolated to the IAC motor.
Engine will also keep the minimum revs at the elevated level during driving.
There are no vac leaks and I have tried another 2 used IAC motors with the same effect.
I have had the IAC disconnected from power during correct cold idling and it will not fluctuate and will idle fine, except understandably low revs when engine gets warm as it requires more air flow when hot.
This proved to me where the issue was, however having tried a few IAC motors I am suspecting this may be a faulty PCM.
Are there any other worthwhile things I could try first?
If it is the PCM, am I able to replace it without linking it to the BCM, do I need to or can I use the chip from the old in the new, and are there any systems that won't function like the stock security system if the PCM were replaced and linked up with the BCM?
Main reason I suspect the PCM is that the engine revs jump distinctly during idle at times like the PCM is managing it and enforcing higher revs where it will remain unless restarted or sometimes revving the engine.
Happy to do some more diagnosis if anyone thinks It worthwhile and has a suggestion...
I have software and cable to monitor sensors and IAC etc.
Thanks in advance.
The engine will rev higher than normal when cold, usually in the range of 1200-1700, typically at 1500 approx, this goes away once the engine comes to temperature or has been turned on and off a few times before driving (takes a fair few tries and a couple mins to settle), during the time the problem exists the revs will fluctuate at times jumping by a couple hundred (usually upwards) also pushing the throttle does at times make the revs sit higher than they were before, though not as high as I pushed them, eg. 1500, rev to 2500, drops back to 1700.
Throttle cable and associated parts are all ok, this seems to be isolated to the IAC motor.
Engine will also keep the minimum revs at the elevated level during driving.
There are no vac leaks and I have tried another 2 used IAC motors with the same effect.
I have had the IAC disconnected from power during correct cold idling and it will not fluctuate and will idle fine, except understandably low revs when engine gets warm as it requires more air flow when hot.
This proved to me where the issue was, however having tried a few IAC motors I am suspecting this may be a faulty PCM.
Are there any other worthwhile things I could try first?
If it is the PCM, am I able to replace it without linking it to the BCM, do I need to or can I use the chip from the old in the new, and are there any systems that won't function like the stock security system if the PCM were replaced and linked up with the BCM?
Main reason I suspect the PCM is that the engine revs jump distinctly during idle at times like the PCM is managing it and enforcing higher revs where it will remain unless restarted or sometimes revving the engine.
Happy to do some more diagnosis if anyone thinks It worthwhile and has a suggestion...
I have software and cable to monitor sensors and IAC etc.
Thanks in advance.