The ECM can control the idle speed by electrically controlling the throttle plate, advancing/retarding the spark timing, or increasing/decreasing the air/fuel ratio. The ability for the ECM to control the throttle plate is performed by the use of the throttle actuator control (TAC) module. This assembly, internal to the throttle body assembly, houses a DC motor along with 2 independent throttle positions sensors, which relay the position of the throttle plate. The throttle plate is held open 7 percent to a mechanical stop by the use of spring pressure for minimum idle air and in the event of a motor circuit malfunction. The ECM monitors the throttle actuator control system for faults in the TP sensors, TAC motor circuit, and for a correlation speed to ensure the idle control is in check. DTC P0507 will set if the actual idle speed is greater than a calibrated amount from the ECM commanded idle speed after a certain period of time.

DTC P0507 will set if the actual idle speed is greater than 200 RPM from the ECM commanded idle speed when:

DTC P0507 diagnostic runs continuously once the above conditions have been met.

P0507 is a type B DTC.

Important: If an EGR, fuel trim, HO2S MAF, misfire, system voltage, or throttle actuator DTC is also set, diagnose that DTC first.

Verify the ECM ability to control engine speed by using the scan tool to perform the ENGINE SPEED CONTROL special function. The test will allow the RPM to be raised or lowered in increments of 25, 100, and 500 RPM. Compare the actual ENGINE SPEED to the DESIRED IDLE SPEED. Both should be within 100 RPM of each other.

Make an underhood visual inspection first. Possible causes of high idle speed: