Originally Posted by VillageT
Look at the large vacuum hose that runs from the IAC to the PC Valve.
No such hose. PCV line runs to the intake manifold. IACV uses a separate passageway within the intake manifold.
As a first step, check the IACV electrical connector and wiring is not damaged and is indeed connected. If it checks out OK, disconnect it after the car has warmed up and then been turned off. After restarting the car, no improvement in idling indicates the valve is stuck or unresponsive.
P1506 - Idle Air Control (IAC) Overspeed Error
This DTC is set when the PCM detects engine idle speed that is greater than the desired rpm.
IAC circuit short to GND
Damaged IAC valve
IAC valve stuck open
Failed EVAP system
Disconnect IAC valve and look for little or no change in engine rpm as an indication of a stuck or damaged valve.