P0507: Idle speed remains higher than a stable commanded target

P0507 is the high-idle counterpart of the documented GM speed-control evaluation. Actual engine speed exceeds desired idle enough that the filtered speed error crosses the published boundary below −182 rpm. The negative sign belongs to this error definition; it is not a negative engine-speed reading.

A requested fast idle is different

The monitor requires coolant above 60°C, more than thirty seconds of running and a commanded-rpm change below 25 rpm. Vehicle speed must be below two km/h, and recent gear or torque-converter changes delay eligibility. A deliberately elevated or rapidly changing target should not be mistaken for unexplained high idle.

It runs every 12.5 milliseconds and reaches a pass/fail report after ten seconds of the qualifying conditions. Off-vehicle service control must be inactive, and the engine must actually be idling rather than in auto-stop.

Diagnose the excess relative to demand

Capture requested and actual rpm alongside throttle, airflow and related diagnostic status. Fuel-trim, purge-flow, misfire and several input faults can inhibit this check. A missing result while those faults are active is not proof that speed control is normal.

Use the applicable idle-system procedure to identify why actual speed stays high. The monitor does not specify a universal throttle-cleaning or adaptation remedy. Verification should show a completed passing high-idle test at a stable target, not only an rpm value that looks familiar.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 318, page 319, page 320. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.