Q: Would you come out and diagnosis a car if I don't know the exact problem

asked by on February 11, 2018

Not sure what it is. The car's gear has seemed to be slipping but was still driveable. Now sometimes it goes in gear and other times not. Sometimes there is a thumping noise when going in gear. The rpm also jumps around. I just had spark plugs put on. Also recently had an oil change & a transmission flush & fill done.

My car has 147000 miles.
My car has an automatic transmission.

Part of the service YourMechanic provides is diagnostic related services as we understand that often times the symptoms you are describing may not be clear and you may not know what may be wrong with the vehicle. 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, making turns (which makes use of the power steering pressure switch) 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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