How to lower the high idle?

2008 CHEVROLET COBALT
120,698 MILES • 2.2L • 4 CYL • 2WD • MANUAL
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AZDANNO04
  • MEMBER
  • 348 POSTS
My check engine light came on and says the Idle Control system is higher than average. I cleaned out the throttle body with the throttle body cleaner and cleaned the Mass airflow with the Mass airflow cleaner. Still have a high idle.
Nov 28, 2021 at 8:34 PM
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STEVE W.
  • ✓ASE Certified Mechanic
  • 15,200 POSTS
  • ASE Certified Mechanic
A common cause for a high idle is a vacuum leak. I would start by looking at all of the vacuum lines for any cracks or damage, even just a loose hose could be the reason. A fast way to check is to use a fuel source like an unlit propane torch or a can of carburetor cleaner. Start the engine and before anything warms up spray the cleaner on a section of vacuum line and listen for the engine sound to change.

These might help:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
https://www.youtube.com/watch?v=4ktw1X4W_-k

As for any adjustments, there are none, the PCM controls all of that. Run through the guide and test and see if you can locate the leak. Don't forget to check things like the brake booster and EVAP lines (the easy way to test those is to unplug them and plug the engine side of the port, if the engine starts to idle slower you found a leak.
Nov 28, 2021 at 10:33 PM
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