The title describes my problem pretty well. I'm driving a manual transmission 2003 Toyota Corolla, and this happens whenever the weather starts getting cold.

The engine revs up fairly high, then goes back down, then back up, etc. The colder the car is, the faster the rate of revving is—until the car warms up. When the car is warmed up, the engine doesn't rev by itself anymore.

This only happens when the car is in neutral or when the clutch is pressed down.

I have no ideas, but some research has told me that it might be a vacuum hose?

  • It probably happens all the time, but the inertia of the car stops it accelerating and decelerating quick enough for you to notice, when it is in gear and being driven. It is normal for the idling RPM to be higher when the engine is cold, but IMO it shouldn't be continually changing from fast idle to normal.
    – alephzero
    Nov 1, 2018 at 17:10


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