DECEL Throttle Control System: Operation
Manifold vacuum is routed through a solenoid vacuum valve, which is normally closed, to the vacuum throttle positioner (modulator).
Power is available to solenoid vacuum valve through an electronic sensor, but the sensor ground circuit is open. When engine speed is higher than a predetermined RPM setting, a signal is sent to the solenoid, which allows manifold vacuum to activate the throttle positioner.
NOTE:
On some models a vacuum switch notifies the sensor when manifold vacuum reaches a predetermined value. The sensor then signals the solenoid to activate the throttle positioner (modulator).
Vacuum pulls the throttle positioner diaphragm, which pushes the throttle to high idle position during deceleration.