Q: Car runs rough in drive but run smooth in neutral

asked by on January 12, 2017

Why does my car run rough in drive and smooth in neutral

My car has 16700 miles.
My car has an automatic transmission.

Hi There, It sounds like you may have a faulty MAP sensor as the car responds to putting it in gear or otherwise putting the motor under load. 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 (i.e. when you put it in drive), 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. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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