DTC P0506: Idle Control System, Rpm Less Than Expected: Notes
WARNING: This page is about a different car, the 2002 Mazda 626. 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 or intake air temperature is less than 14°F (-10°C), PCM will not monitor this circuit.