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Q: My car revs uo and down when below when below 2000 rpm above that it works fine

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Had this problem for quite some times first we believed the timing was wrong with our car so we check that and it was fine. also changed the coils and plugs and and the plastic cover that goes with the coils. Changed the throttle position sensor as well as the intake and other minor electrical parts with no success. We also tried running the car with the position sensor and sometimes the cam sensor unplugged and there seem to be no change whats so ever. -please help Thank you
My car has an automatic transmission.

A: Hi there. As you already know, replacing co...

Hi there. As you already know, replacing components without diagnoses can be expensive and time consuming without resolution. Performing a fuel pressure test may identify whether the fuel pressure regulator is causing the surging rpm (revolutions per minute) below 2,000rpm. A vacuum leak could also cause an unstable engine speed. Assuming, the check engine/service engine soon light is not coming on, leads me to believe the ECM (engine control module)/computer is not recognizing the fault. A faulty IAC (idle air control) valve or faulty EGR (exhaust gas recirculation) valve could cause an unstable engine speed. Proper diagnoses needs to be performed to avoid unnecessary repairs. I recommend having your vehicle’s surging rpm below 2,000rpm be diagnosed and repaired by a certified technician, such as one from YourMechanic.

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