DTC P0505: Idle Control System: Description

The DTC P0505 Idle Air Control (IAC) System diagnostic observes engine speed in order to monitor the operation of the IAC valve. The Powertrain Control Module (PCM) controls engine idle speed with the idle air control valve. To increase the idle speed, the PCM pulse width modulates the OPEN solenoid within the IAC valve. This action turns a cylinder within the IAC valve, allowing air to bypass the throttle plate. The PCM regulates fast idle speed via the IAC valve by increasing the opening of the air bypass port. PCM regulates slow idle speed via the IAC valve by decreasing the opening of the air bypass port.