Q: Car jerks at a stop, only when AC is turned on.

asked by on November 13, 2017

I've been having this issue for months now. Whenever I come to a stop, whether it be a stop sign or red light, my car jerks and kicks, this ONLY happens when the AC is turned on, I've driven the car with the AC off numerous times and it never has that issue. So far I have replaced the mass air flow sensor, the idle air control valve, PCV valve, the throttle position sensor, and I have also cleaned the throttle body as best I could, none of this has solved my problem.

My car has 118000 miles.
My car has an automatic transmission.

As you may know, the AC system puts an additional strain on the motor. The air conditioning compressor requires torque from the belt system on the engine to power it. When the AC is off, the compressor clutch does not activate, meaning the AC is not straining the engine. When the AC is on, the compressor clutch activates, wherein the drive belt on the engine now turns the compressor which in turn is compressing refrigerant so you can be nice and cold. The Idle Control Actuator is what controls the engine idle. When the AC kicks in, the engine will drop some RPM, and the actuator opens to allow more air into the engine. When you are at speed, the throttle is open from the accelerator pedal under your foot. the Idle control actuator is not active at this time. I would suggest having an exert from YourMechanic come to your location to take a look at the vehicle to verify what may be causing the rough idle.

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