Conditions for Setting the DTC: P0506
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The actual engine speed is less than the desired idle speed by at least 100 RPM for 4 seconds or for a cumulative of 50 seconds.