When I start my car, the RPMs go up and down, over and over. Also, when I turn off my car, it makes a noise.
This is most likely caused by a faulty Idle Air Control valve (IAC valve). This valve regulates the speed of the engine’s idle by creating a controlled vacuum leak in the intake manifold. It is also possible that there may be a vacuum leak that is simulating a bad IAC valve. I would ask for help from one of the mechanics at YourMechanic to come to you and diagnose why your car does not maintain a consistent engine idle speed.
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