2010 HHR 2.2L P0507 High Idle Code: Troubleshooting After Engine Replacement
I recently replaced the engine in my 2010 HHR with a stock 2.2L unit from the same model year Chevrolet Cobalt. However, I'm still experiencing a persistent P0507 diagnostic trouble code indicating high idle. The vehicle idles smoothly at 800 RPM when cold, but after driving and coming to a stop in park, it briefly runs around 1400 RPM for up to 30 seconds before settling back to 800 RPM. I've already replaced the throttle body and performed a thorough vacuum leak check with no positive findings. I've also attempted idle learn reset procedures, but none have been successful. The engine is bone stock—no modifications or aftermarket parts—and the replacement motor was sourced from a matching-year Cobalt, differing only in minor mounting components and fuel injectors. I'm seeking advice on how to properly diagnose and resolve this P0507 issue, especially since I don't currently have access to a bi-directional scanner for real-time sensor data or idle control adjustments.
A new engine in a 2010 HHR? Confirming it's the original engine with no modifications. Throttle linkage binding and vacuum leaks—especially within EVAP systems—are common culprits. I recommend checking the idle air control (IAC) circuit using a bi-directional scanner to verify command signals and sensor feedback. Reviewing freeze frame data during the high-idle event could provide critical insights into when and how the issue occurs. This would help pinpoint whether it's a sensor reading, actuator response, or system miscommunication.