Q: There is a couple hiccups in acceleration ONLY on FIRST start up and ONLY when put into reverse before drive. 2004 Hyundai santafe

asked by on September 16, 2017

There is a couple of hiccups in acceleration ONLY on FIRST start up and ONLY when put into reverse before drive. It happens every time without fail. It will not do it for the remainder of the drive. It is extremely noticeable. I did just drain and fill the automatic transmission fluid with authentic Hyundai AT fluid. But level is good. Thank you for your time.

My car has 73000 miles.
My car has an automatic transmission.

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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