W 250 Pickup V8-5.9L VIN Z (1991)
Idle Speed/Throttle Actuator - Electronic: Description and Operation
Throttle Body
The Idle Speed Control (ISC) actuator is controlled by the engine controller, and mounted to the side of the throttle body. The throttle lever, when the
engine is at idle, rests against an adjustment screw at the end of the actuators plunger. The ISC motor is used to set throttle stop angle during
deceleration, and it controls the engine idle speed by extending or retracting its plunger.
The engine controller receives input signals from certain sensors and switches indicating certain conditions. The engine controller applies the ground
and the power to the ISC motor to adjust the actuator position for certain driving conditions. The ISC motor also contains the idle contact switch.
NOTE: Do not try to correct a high idle speed condition by changing the adjustment screw position.
When the engine is shut off, the engine controller fully extends the ISC plunger for a fast idle speed for the next engine start up. If the adjustment screw
is adjusted it will not affect a warm engine idle speed, but will in fact cause cold start driveability problems. For the ISC motor adjustment refer to
Powertrain Management/Computers and Control Systems/Idle Speed Throttle Actuator - Electronic/Adjustments.