IAC problems 2001 LS1
03-07-2012, 07:53 PM
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IAC problems 2001 LS1 I had a sudden intermittent high idle problem (2500 RPMs) which would sometimes happen after driving for a while, and would sometimes happen immediately. This went on for a few weeks and was very annoying. Car only has exhaust modded.
Obviously something this large could be an unmetered air leak, but my computer showed that it was indeed being metered,but that the IAC was also working as commanded. I cleaned the IAC and the problem still happened.
When the car was idling properly, I unplugged the IAC. It has been unplugged for a few months and the problem has not happened since.
Has anyone heard of an IAC that was actually malfunctioning, but the computer was still reading it as working as commanded?
I want to buy a new IAC, but I have heard that they don't fail very often. Because the problem has not come back, I am 99% sure that it was the problem. However, it is weird though that commanded IAC and actual IAC were in-line when the high idle problem would occur.
Obviously something this large could be an unmetered air leak, but my computer showed that it was indeed being metered,but that the IAC was also working as commanded. I cleaned the IAC and the problem still happened.
When the car was idling properly, I unplugged the IAC. It has been unplugged for a few months and the problem has not happened since.
Has anyone heard of an IAC that was actually malfunctioning, but the computer was still reading it as working as commanded?
I want to buy a new IAC, but I have heard that they don't fail very often. Because the problem has not come back, I am 99% sure that it was the problem. However, it is weird though that commanded IAC and actual IAC were in-line when the high idle problem would occur.
03-07-2012, 08:24 PM
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As far as I can tell, there is no "actual" IAC reading in the
sense of a measured true position. IAC only has the 4
stepper phases going to it and no feedback. Any IAC
position value has to be derived by PCM "bookkeeping"
after a "home event" puts it to a known position.
There are IAC drivers in the PCM and they can go bad,
although there isn't much reason for them to. Could be
a PCM brain-fart. Or could be there is some kooky idle
air, throttle cracker, throttle follower cell that asks
for big air, but only gets stepped into on some rare
circumstance. I dunno.
sense of a measured true position. IAC only has the 4
stepper phases going to it and no feedback. Any IAC
position value has to be derived by PCM "bookkeeping"
after a "home event" puts it to a known position.
There are IAC drivers in the PCM and they can go bad,
although there isn't much reason for them to. Could be
a PCM brain-fart. Or could be there is some kooky idle
air, throttle cracker, throttle follower cell that asks
for big air, but only gets stepped into on some rare
circumstance. I dunno.
03-07-2012, 08:30 PM
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Thank you for the reply! When the car was idling properly, I could use the software to increase the IAC as high as it would let me, and it would only go up to about 1700RPMs IIRC.
Not the 2500 that would happen when the car acts up.
Since it doesn't have any real measured true position feedback, I feel better about replacing it. There are some cheapo's out there for $25 bucks. I'll go with one of those and see what happens.
Thanks again for the more detailed info.
Not the 2500 that would happen when the car acts up.
Since it doesn't have any real measured true position feedback, I feel better about replacing it. There are some cheapo's out there for $25 bucks. I'll go with one of those and see what happens.
Thanks again for the more detailed info.
