K 2500 Suburban 4WD V8-454 7.4L VIN N TBI (1995)
Idle Speed Control Actuator System
ISC 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 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.
4. Checks to see cause of no vacuum source.
5. Checks idle speed control solenoid and connections.
