steady idle ?
Thread Starter
Burning Brakes
Joined: May 2013
Posts: 1,249
Likes: 142
From: Lynn MA
steady idle ?
My 99 C5 vert 6 speed on start up seems to be searching for the proper idle speed. It fluctuates between 500 to 850 rpm until it is up to operating temp. Once warmed up it is good to go. I've cleaned the MAF and Throttle body and replaced the throttle position sensor already. Is there an idle air control valve also ? I could really use some help.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,061
From: Cape Coral, Florida
Had the battery been disconnected when you noticed the unstable idle ??…sometimes after reconnecting the battery an “idle relearn” may have to be done…you may have a vacuum leak but it’s hard to say…if you have a scan tool that you can look at things like O2 sensors, fuel trims, MAF and MAP sensor data PIDS it’s only a guess…and no IAC !!
Last edited by C5 Diag; Jul 31, 2023 at 12:13 PM.
Racer
Joined: Oct 2021
Posts: 324
Likes: 157
From: Maine
Not sure this will help but I had a strange idle issue that was the same once up to temp. I replaced my knock sensors and cleaned up lots of oil in my intake and installed new intake gaskets.
The oil pressure sensor had been replaced before I go the car. After the work was done I had working knock sensors (that was the plan) but the strange idle issue was fixed.
If I had to guess I would say it was the new intake gaskets fixed the idle, so maybe once your car is up to temp with all the things expanded your intake leak is gone.
I recall reading about how to check for intake leaks by spraying something in the suspect area and if you idle changes X marks the spot. Good luck hope this helps
The oil pressure sensor had been replaced before I go the car. After the work was done I had working knock sensors (that was the plan) but the strange idle issue was fixed.
If I had to guess I would say it was the new intake gaskets fixed the idle, so maybe once your car is up to temp with all the things expanded your intake leak is gone.
I recall reading about how to check for intake leaks by spraying something in the suspect area and if you idle changes X marks the spot. Good luck hope this helps
Drifting
Joined: Mar 2018
Posts: 1,365
Likes: 414
From: New Jersey
Not sure this will help but I had a strange idle issue that was the same once up to temp. I replaced my knock sensors and cleaned up lots of oil in my intake and installed new intake gaskets.
The oil pressure sensor had been replaced before I go the car. After the work was done I had working knock sensors (that was the plan) but the strange idle issue was fixed.
If I had to guess I would say it was the new intake gaskets fixed the idle, so maybe once your car is up to temp with all the things expanded your intake leak is gone.
I recall reading about how to check for intake leaks by spraying something in the suspect area and if you idle changes X marks the spot. Good luck hope this helps
The oil pressure sensor had been replaced before I go the car. After the work was done I had working knock sensors (that was the plan) but the strange idle issue was fixed.
If I had to guess I would say it was the new intake gaskets fixed the idle, so maybe once your car is up to temp with all the things expanded your intake leak is gone.
I recall reading about how to check for intake leaks by spraying something in the suspect area and if you idle changes X marks the spot. Good luck hope this helps
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There is an idle relearn procedure in the factory service manual. My engine is modded, so maybe that's why it worked so well for me. But it made my idle sound like a milder cam was installed, and you could hear the change immediately.....
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From: Cape Coral, Florida
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