Q: Engine stalls under braking

asked by on March 10, 2017

van runs fine through gears but when braking coming to a stop sputters and cuts out. will then start up and accelerate perfect did a tune up change throttle body and purge silenoid. no codes stored or present doesnt cut out and runs perfectly except under braking

My car has 142000 miles.
My car has an automatic transmission.

What you are describing sounds like possibly 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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