Conditions for Setting the DTC (w/TAC): P0506
WARNING: This page is about a different car, the 2008 Suzuki Swift +, 2008 Pontiac Wave, and 2008 Chevrolet Aveo. 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 10 seconds.