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Q: Engine rpm not steady at 40-55 mph

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When holding throttle steady in the 40-55mph range the engine and tachometer is slightly moving up or down. If I barely increase or decrease throttle it stops. Tried the tc lockup test by hitting the brakes while issue is present with no change. Brought to my mechanic and he reflashed the ecm but problem still persists. Changed plugs and wires with no change. The car seems to be slightly lower than normal on power and seems to idle a little tougher than normal but this may be because I'm watching it closely.

My car has 83000 miles.
My car has an automatic transmission.

A: This is a common sign of a failing throttle...

This is a common sign of a failing throttle position sensor. The throttle position sensor (TPS) is a sensor used to monitor the throttle position of a vehicle. The sensor is usually located on the butterfly spindle/shaft so that it can directly monitor the position of the throttle. This sensor relays the position of the throttle plate (also called the butterfly) relative to your foot's position on the gas pedal and associates the two in the ECU. The ECU then makes the direction to supply more or less fuel to the motor. When this sensor is not working properly, this can cause intermittent responses when applying the gas pedal. I would suggest having a professional from YourMechanic come to you home to diagnose and replace this sensor.

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