Monitor Description
The idle speeds are determined depending on the volume of air that passes through the intake air control (IAC) valve. When the volume is large, the idle speed becomes higher. When the volume is small, the idle speed becomes lower. The IAC valve controls the air volume that bypasses the throttle valve. The ECM sends duty signals to the IAC valve and drives the IAC valve stepper motor to regulate the air volume that bypasses the throttle valve.
Although the ECM regulates the idle engine RPM with the feedback control in several vehicle stopped, actual idle RPM does not reach the targeted RPM and a learned valve angle of the idle air control (IAC) remains at the maximum or remains at the minimum, the ECM determines to detect malfunction in the IAC system.
Example:
If the difference between the targeted and actual idle engine RPMs exceeds 200 RPM (*1) with the vehicle stopped in an idle, and this occurs 5 times, or if the learned value angle of the ISC remains at its maximum or minimum angle for 5 seconds, P0505 is detected.
P0511 is detected as an open/short circuit in the IAC if the rate of duty signal input to the IAC valve has stuck at 0 or 100 %.
*1: Threshold RPM is varied by an engine load.