Possible causes

– Faulty Idle Air Control (IAC) valve
– Idle Air Control (IAC) valve harness is open or shorted
– Idle Air Control (IAC) valve circuit poor electrical connection

Tech notes

The P1506 code means that the engine idle is out of factory specification. Sometimes the Idle Air Control (IAC) may have carbon built up. Disconnect the car battery, remove the valve, clean, re-install valve, and drive the vehicle for about 5 minutes with the headlights and A/C ON to get the idle relearned.
If the problem persist, the IAC valve may need to be replaced.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1506 MAZDA Description

The P1506 code is set when the Engine Control Module (ECM) detects engine idle speed that is greater than the desired rpm.

MAZDA Technical Service Bulletins for P1506 code