Conditions for Setting the DTC: P0506
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects the actual idle speed is at least 100 RPM below the desired idle speed for greater than 19 seconds.