A/C Idle-Up Circuit Check (Equipped With A/C)

A/C amplifier sends an idle-up signal to ECM when A/C compressor clutch is in operation. ECM will activate Idle Speed Control (ISC) motor. ISC opens the throttle plate to control engine speed to prevent rough idle or stalling condition. To check A/C idle-up circuit see appropriate CHART C-1B under DIAGNOSTIC CHARTS.