DTC P0506: Idle Control System - Rpm Less Than Expected: Notes
WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If atmospheric pressure is less than 21.3 in. Hg (72.3 kPa) or intake air temperature is less than 14°F (-10°C), PCM cancels diagnosis of P0506.