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 2005 Mercury Sable, 2005 Mercury Mountaineer, 2005 Mercury Monterey, 2005 Mercury Montego, and 2005 Mercury Mariner. However, it is still accessible from the selected car via links, so may be relevant.

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

For Vehicles With Electronic Throttle Control (ETC)
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:	Air intake restriction Exhaust restriction Engine mechanical fault. Damaged electronic throttle body (ETB) Damaged PCM
Diagnostic Aids:	This DTC is informational only and it 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 retest.
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:	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.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
Vehicles With Electronic Throttle Control (ETC)	Refer to the Description, Possible Causes and Diagnostic Aids for the DTC.
All others	GO to KE: Idle Air Control (IAC) Valve STEP KE1.