K 3500 Truck 4WD V8-454 7.4L (1994)
Idle Speed Control Actuator Circuit
Circuit Description:
The idle speed control actuator system assists the idle air control system in controlling the idle speed, primarily at cold temperatures. The idle speed
control actuator is a vacuum operated device which opens the throttle slightly (2 to 3 degrees of angle) to increase the cold engine idle speed, to improve
the mixing of the air and fuel, and to allow lower warmed up engine idle speeds. The idle speed control actuator is controlled by the idle speed control
actuator solenoid, which is controlled by the control module. To increase the idle speed, the solenoid is turned "OFF," and no vacuum is routed to the
idle speed control actuator, allowing it to open the throttle slightly. To decrease the idle speed, the solenoid is turned "ON," and vacuum is routed
through the solenoid to the idle speed control actuator, allowing the throttle to fully close.
In conjunction with the idle speed control actuator system, the idle air control system continuously monitors and controls the engine idle speed to the
desired idle speed. A Tech 1 scan tool will read the control module commands to the idle speed control actuator system.
Chart 1 Test Description: Number(s) below refer to circled number(s) on the diagnostic charts.
1. Checks to see if a vacuum source is present.
2. Checks to see if idle speed control actuator solenoid is commanded "ON."
3. Checks for power to the solenoid, the ground circuit, the connections at the idle speed control actuator solenoid and the solenoid itself.
Diagnostic Aids: Check all connections. If OK, refer to DIAGNOSIS BY SYMPTOM/ INTERMITTENTS See: Computers and Control
Systems/Testing and Inspection/Symptom Related Diagnostic Procedures/Intermittent Condition .
