Q: Car RPM drops on AC, stalling the car.

asked by on March 14, 2017

My Nissan Sunny's RPM drops dramatically on AC. We had the compressor and the wirings checked but the issue remains. My mechanic told me we need to change an "auto choke sensor" , which according to him regulates RPM. Another mechanic told me to change the whole throttle body.

I just want an expert opinion on what an auto choke sensor is, and will it indeed help regulate RPM, before I go ahead and spend money on the problem. Im a student and so I want to make sure Im spending my money on the right thing.

PS. The RPM also drops when braking or turning the steering wheel, but the car only stalls on AC when I lift my foot off the accelerator.
My car has a manual transmission.

Hi There, This may be a sign of a faulty MAP sensor as the vehicle responds adversely to a load put on the motor (i.e. putting it in gear, turning on AC or engaging the brakes). The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine takes in more air, which requires more fuel to keep the air/fuel ratio in balance. When the computer reads a heavy load signal from the MAP sensor, it adjusts the fuel mixture to slightly more rich than normal so the engine can produce more power. The computer will then retard (back off) ignition timing slightly to prevent detonation that can damage the engine and decrease performance. This may also be caused by other closely related components such as a dirty or failing mass air-flow sensor, a faulty throttle position sensor or potentially a vacuum leak. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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