DTC P0505: - Idle Air Control (IAC) System

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 P0505: - IDLE AIR CONTROL (IAC) SYSTEM

For Vehicles With an Idle Air Control (IAC) Valve
Description:	The powertrain control module (PCM) attempts to control engine speed during the key on, engine running (KOER) self-test. The test fails when the desired RPM could not be reached or controlled during the self-test.
Possible Causes:	IAC circuit open VPWR to IAC solenoid open B+ or VPWR to IAC solenoid open Air inlet is plugged IAC circuit shorted to PWR Damaged IAC valve
Diagnostic Aids:
For All others
Description:	The powertrain control module (PCM) attempts to control engine speed during the key on, engine running (KOER) self-test. The test fails when the desired RPM could not be reached or controlled during the self-test.
Possible Causes:	Failure mode effects management (FMEM) condition is present Intake air restriction Exhaust restriction Sludged throttle body Vacuum leaks 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, vacuum leaks, 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 .