How the Circuit Works
Idle Speed ControlHOW THE CIRCUIT WORKS
The Idle Speed Control System consists of an Idle Speed Module, a Coolant Temperature Switch and the Idle Speed Control Motor. This system controls five engine control functions.
- No Touch Starting (warm engine only)
- Cold engine Idle Speed Control
- Dashpot
- Warm engine Idle Speed Control anti-diesel- engine shutdown
No Touch Starting (Warm Engine Only)
The throttle is prepositioned by the Idle Speed Control Motor. Prepositioning of the plunger to the extended position allows for quicker starting for a warm engine.
Cold Engine Idle Speed Control
On start-up if the coolant temperature is less than 128°F the temperature switch will be open and the computer will set the curb idle speed at 1200 rpm. If the engine coolant switch isn't closed after 10 minutes the computer sets the Warm Idle Speed.
Dashpot
On driveway the computer detects the closure of the idle tracking switch (part of the Idle Speed Control Motor) waits two seconds then extends the plunger until the throttle is contacted or fully extended position is reached. When decelerating the ITS switch opens and the computer delays for 300 milliseconds then returns to the curb idle set point.
If a long deceleration is encountered the computer attempts to reduce the engine's speed unsuccessfully and then will retract as far as the fail-safe screw.
Warm Engine Idle Speed Control
In conditions with the coolant temperature above 128°F the computer will maintain an idle speed of 800 rpm under all load conditions.
Anti-diesel Engine Shutdown
When the ignition key has been turned OFF, the computer will retract the plunger for two seconds to prevent dieseling, hold in that position for two seconds and then extend out for the next engine crank.