Q: My car keeps cutting off when I put it in reverse and sometimes when it idles.

asked by on January 03, 2017

So sometimes when I put it in reverse it cuts off and when it idles. My girlfriend was going 45 and the engine cuts off. It's not a bad alternator cause I check that. The spark plugs have been replaced. So I knows it's not those two things. I'm thinking it's a bad fuel filter or fuel pump. Maybe a bad air filter. Oh another thing. When I hit the gas the engine cuts off for a second and starts to move the car.

My car has 150000 miles.
My car has an automatic transmission.

Hi There, Based upon what you are describing and how the car responds to load, it sounds like you may have a faulty MAP sensor. 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]((https://www.yourmechanic.com/services/manifold-absolute-pressure-sensor-map-sensor-replacement), 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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