High idle while rolling
Thread Starter
Teching In
Joined: Jun 2021
Posts: 16
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From: Maryland
High idle while rolling Having an interesting issue with my idle. When I’m stopped the car idles perfectly however when rolling the idle goes up to almost 2k rpm. When I come to a stop the car idles perfectly again. I’ve checked for vacuum leaks and have not been able to find any. Also if it was a vacuum leak wouldn’t the rpm’s rise even while not rolling? I have a small coolant leak but I’d imagine that would have no effect on the idle. Any help would be appreciated thank you
Thread Starter
Teching In
Joined: Jun 2021
Posts: 16
Likes: 0
From: Maryland
-Prc 227 ported heads
-Texas speed magic stick 3 cam
-fast 92 intake
-slp headers
-slp loudmouth 2 exhaust
Its a m6 car and was tuned 5 months ago using a speed density tune.
TECH Resident
Joined: Jun 2013
Posts: 809
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From: Nebraska, The Good Life
For both of you, it has been doing it all along and you only recently noticed it. The computer will keep the idle slightly higher if the car is still moving assuming you are going into a gear and will be moving away. Kind of a crude rev matching feature.
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No one recently notices something with their car that has been doing something " all along".. any of us car guys know every little noise and vibration our cars make and when somerthing is different.
2k RPM is not "slightly higher" either.
MAF tune is better than just Speed Density, I tune all my stuff with both.
A completely stock car will be a vac leak somewhere.
2k RPM is not "slightly higher" either.
MAF tune is better than just Speed Density, I tune all my stuff with both.
A completely stock car will be a vac leak somewhere.
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It would also be interesting to look at the throttle cracker tables, as they can do what you describe, if they're tuned wrong enough. So can throttle follower, but that takes more effort.
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I had this issue when I swapped out my heads, cam, intake, etc. on my 2000 Z28. The evap control valve that plugs into the intake and runs to the charcoal canister was the issue. I plugged it into the intake but didn’t plug in the solenoid. This valve apparently is a “fail to open” and basically I had a vacuum leak that went all the way to my charcoal canister!
The EVAP Solenoid there on the Intake stays closed until the PCM senses too high of pressure in the Gas Tank, the it commands it to open as well as the one on the Charcoal Canister opens and that pulls the pressure out.
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Think about a cable body like on our f bodies. If the there’s a failure like the cable breaks the spring on the throttle body will close the throttle blade. This is called fail to close.