Monitor Description
The idle speed is determined depending on the volume of air that passes through the ISC valve. When the volume is large, the idle speed is higher. When the volume is small, the idle speed is lower. The ISC valve controls the volume of air that bypasses the throttle valve. The engine control module (ECM) sends duty signals to the ISC valve and drives the ISC valve to determine the volume of air that bypasses the throttle valve.
Although the ECM regulates the idle engine RPM with the feedback control in several vehicle stopped, actual idle RPM dose not reach the targeted RPM and a learned valve angle of the idle speed control (ISC) remains at the maximum or remains at the minimum, the ECM determines to detect malfunction in the ISC system. If the rate of duty signal input to the ISC valve is stuck to 0 or 100 %, the ECM interprets it as an open/short circuit in the ISC valve and sets a DTC.
Example:
If then RPM difference between the target RPM and actual RPM exceeds 200 rpm (the threshold is varied by an engine load) with the vehicle stopped in the idle and this occurs 5 times.