Idle surge...?
Thread Starter
Instructor
Joined: May 2006
Posts: 154
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From: Kingsland Georgia
Idle surge...?
96 LT 4...Car runs great except when at idled...a surge ...irritating.. I’ve done lots. Actually sold car but trying to help new owners...Today was said that mechanic unplugged MAF and idle fine. Replaced and back to surge. Unplugged IAC vale...idle fine... replaced and surge...I had done all this before...can this be a ground issue...? Thoughts...ECM...?? Lots of time spent on this....!!! Car is sharpe...only issue...one clue is as long as there is a digit on speedo idle is fine...but when hits 0...the search starts..??
Last edited by Capt. Ron; Sep 10, 2020 at 12:42 AM.
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
96 LT 4...Car runs great except when at idled...a surge ...irritating.. I’ve done lots. Actually sold car but trying to help new owners...Today was said that mechanic unplugged MAF and idle fine. Replaced and back to surge. Unplugged IAC vale...idle fine... replaced and surge...I had done all this before...can this be a ground issue...? Thoughts...ECM...?? Lots of time spent on this....!!! Car is sharpe...only issue...one clue is as long as there is a digit on speedo idle is fine...but when hits 0...the search starts..??
If I had to throw a part at it, I would try the MAF first. It has been known to cause idle problems when failing on older systems. I would suspect similar results here as well. I suggest you get some data first. It will probably be cheaper than buying multiple parts.
Thread Starter
Instructor
Joined: May 2006
Posts: 154
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From: Kingsland Georgia
Done that...
MAF replaced, IAC replaced, TPS replaced, some coolant sending unit replaced...I don’t have a scanner I can get that data...is there someone on here that re-flashes ECM boards for 96 LT4...?
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
Race Director
Joined: Jan 2012
Posts: 17,062
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From: United States
The IAC counts will only show you what the ECM is sending to the IAC. Not what the IAC is actually doing.
I would replace IAC...IACs go bad and its not recommended to take them out and clean them.. Easy to break, and hard to find gasket..
I would replace IAC...IACs go bad and its not recommended to take them out and clean them.. Easy to break, and hard to find gasket..
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Drifting
Joined: Jun 2018
Posts: 1,678
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From: Michigan
There are many reputable sites with instructions on how to clean them.
TPI/LT1 guys have been cleaning IACs and their housings for decades.
Not that we always do what is "recommended", but I wouldn't fear cleaning it and putting it back in. A pretty cheap effort before buying an IAC motor.
Just curious, do you have any documentation that shows we shouldn't be cleaning the seat and spring of our IACs?
Last edited by KyleF; Sep 11, 2020 at 11:15 AM.
Race Director
Joined: Jan 2012
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From: United States
I have taken them out and cleaned many an IAC passage, Pentile, and throttle body.
There are many reputable sites with instructions on how to clean them.
TPI/LT1 guys have been cleaning IACs and their housings for decades.
Not that we always do what is "recommended", but I wouldn't fear cleaning it and putting it back in. A pretty cheap effort before buying an IAC motor.
Just curious, do you have any documentation that shows we shouldn't be cleaning the seat and spring of our IACs?
There are many reputable sites with instructions on how to clean them.
TPI/LT1 guys have been cleaning IACs and their housings for decades.
Not that we always do what is "recommended", but I wouldn't fear cleaning it and putting it back in. A pretty cheap effort before buying an IAC motor.
Just curious, do you have any documentation that shows we shouldn't be cleaning the seat and spring of our IACs?
I have had my LT1 since 96, and have had L98s too.. Just need to be delicate with it as it can cause hate and discontent with the engine if broken.
Up through 93, you could use a ohm meter across two of the connectors inside, and it would tell you if it was bad electronically.. Not sure of 96-97 LT1s.
Drifting
Joined: Jul 2004
Posts: 1,344
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From: MA
The IAC is basically just a stepper motor, it can be cleaned carefully with either electronic contact cleaner or Mass Air Flow Sensor safe cleaner. These two chemicals will not bother any of the windings or plastic inside the IAC.
-Don't use Brake Clean!
-Do replace the O-ring on the IAC, it could be bad causing your idle issues (if worn it will cause the idle to hunt and not allow the IAC to meter properly).
-Don't use Brake Clean!
-Do replace the O-ring on the IAC, it could be bad causing your idle issues (if worn it will cause the idle to hunt and not allow the IAC to meter properly).