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Q: My car runs rough at idle, stalls at idle, surges, and idles at 40 miles an hour

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What do I need to replace to stop rough idling, stalling ,fast idling (40mps) and surging. Already replaced throttle body sensor.

My car has 75000 miles.
My car has an automatic transmission.

A number of components or faults can cause your issues. A vacuum leak can cause your issues. Depending on the vehicle, components such as the mass airflow sensor, throttle position sensor, coolant temperature sensor, and a number of others can be the cause. Since randomly replacing parts can get expensive as most electronic components are not returnable once installed, having a certified technician, such as one from YourMechanic, diagnose the stalling/surging is the best place to start.

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