The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
A spark plug is fouled.
Time to have the O2 sensor after the cat tested. It should show steady voltage ( 200MV depending on the vehicle). If the voltage varies (100MV to 600MV) it is time to replace the cat. Have all the O2 senors tested while your at it.
P1506 Idle Air Control System Overspeed Error (Ford)
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
I would start out by cleaning the IAC valve and it's port.
Good luck and let us know.
Wednesday, February 22nd, 2006 AT 7:23 PM