Q: Acceleration trouble.

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I can't figure this out. My fiance's altima will not do more than 2500 rpm. As soon as u put it in reverse or drive it stalls out. It sometimes stalls out at red lights. Does a lot of jerking feels like its choking. I changed fuel filter and pump and pump strainer. It throwing two codes one for the MAF sensor and something about second gear ratio or something but i know that ain't the issue . So i changed the MAF sensor and air filter. Still nothing. It sometimes backfires right where the air filter is. I read numerous different things but idk what to do and I'm pretty good at figuring cars out. So could u please give me any suggestions?

My car has 122470 miles.
My car has an automatic transmission.

Hello, It sounds like the vehicle responds adversely to various loads being put on it such as sitting at the stop light and being put into gear. Both of these situations cause a load to be put on the motor that is more than when the motor is just sitting in park or neutral and idling. The MAP sensor is something that helps to relay information to the computer which uses this to adjust according to the load put on the motor. 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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