My Toyota corolla 2008 is idling rough when I on AC, but when the car is moving everything becomes fine. I just replaced a clean intake manifold. What could be the problem? Any idea plz.

  • Get an OBD II reader with PID capability and verify that the "AC COMPRESSOR ON" signal is registering. This signal increases idle and compensates for AC load. It's possible an electrical connection was disturbed when replacing the intake manifold. It's also possible you now have a small vacuum leak.
    – SteveRacer
    Jul 18, 2018 at 1:41

2 Answers 2


I'd try cleaning the throtlle body. I've seen noticable improvements in idle smoothness after cleaning all the deposits from it. Use carb cleaner, paper towels, and q-tips. Try to avoid spraying a bunch of carb cleaner down the intake, spray it in the paper towel or q-tip and use that to wipe off the deposits. Make sure to get both sides of the butterfly, it's hard to reach.


There are a lot of reasons why you are experiencing a rough idle on your car. Try to check if you have a dirty fuel injector, clogged air filters, bad spark plugs, and exhaust system issues to have it fixed.

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