Idle Speed/Throttle Actuator - Mechanical: Description and Operation

Fig. 1 Idle Control System (A/T only):

AUTOMATIC TRANSMISSION

The carburetor mounted throttle controller is a spring loaded vacuum motor that is used by the PGM unit to maintain a stable idle under various engine load conditions. In conjunction with frequency solenoid C, it opens and closes the throttle valve slightly to maintain an idle speed of 730 rpm. When engine temperature is above 140°F (60°C) and engine speed varies from 730 rpm frequency valve C is used. When deenergized, vacuum is allowed to the throttle controller, which pulls the throttle open a preset amount. When the solenoid is powered, it vents vacuum normally applied to the throttle controller. The spring pressure of the throttle controller diaphragm then pushes the throttle closed slightly. For additional information on frequency valve C refer to COMPUTERIZED ENGINE CONTROLS.

Fig. 30 Dashpot System Diagram (Manual Transmission):

MANUAL TRANSMISSION

The carburetor mounted throttle controller serves as both a dashpot and a cranking throttle opener. The supply vacuum line has a check valve installed with a small metered orifice. During deceleration it prevents rapid shutting of throttle plate. During engine cranking low manifold vacuum allows the spring loaded controller to partially opens the throttle plate for improved starting.