DTC P0506: - Idle Air Control (IAC) System Rpm Lower Than Expected

WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2009 Mercury Mountaineer, 2009 Mercury Milan, 2009 Mercury Mariner, 2009 Mercury Grand Marquis, and 2009 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0506: - IDLE AIR CONTROL (IAC) SYSTEM RPM LOWER THAN EXPECTED

For Vehicles With an Idle Air Control (IAC) Valve
Description:	This DTC is set when the powertrain control module (PCM) detects an engine idle speed that is less than the desired RPM.
Possible Causes:	IAC circuit open Air inlet is plugged B+ or VPWR to IAC solenoid open Damaged or incorrect IAC valve IAC valve stuck closed VPWR to IAC solenoid open IAC circuit shorted to PWR
Diagnostic Aids:	Disconnect the IAC valve and look for little or no change in engine RPM as an indication of a stuck or damaged valve.
For All others
Description:	This DTC is set when the powertrain control module (PCM) detects an engine idle speed that is less than the desired RPM.
Possible Causes:	Intake air restriction Vacuum leaks Exhaust restriction Engine mechanical concern Sludged throttle body Damaged electronic throttle body (ETB) Damaged PCM
Diagnostic Aids:	This DTC may be accompanied by other DTCs. Diagnose other DTCs first. If other DTCs are not present inspect the intake air system for air restrictions and damage. If no concerns are present, clear the DTC and carry out the KOER self-test.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
Ranger	GO to Pinpoint Test KE .
All others	GO to Pinpoint Test HU .