Throttle Control System

Engines W/Throttle Body Injection
This system consists of a dashpot diaphragm and diaphragm rod connected to the throttle valve, which functions as a cranking opener. During starter cranking, the spring in the dashpot diaphragm opens the throttle valve a sufficient amount to assist starting of the engine. Once the engine is started and is idling, intake manifold vacuum acts on the dashpot and pulls the diaphragm rod, which then positions the throttle valve in the correct idle position.
Engines W/Multi-Point Injection
This system consists of a dashpot with duel diaphragms, a diaphragm rod, and a dashpot control solenoid.
The bottom half of the diaphragm (diaphragm B), is used to increase the air flow rate at low ambient temperatures, enabling proper fast idle operation. When the dashpot control solenoid is activated at low ambient temperatures, intake manifold vacuum is blocked off to diaphragm B. This allows the throttle valve to be held open a specific amount by the position of the diaphragm rod.
The top half of the diaphragm (diaphragm A), is used to slow the closing of the throttle valve during shifting or deceleration to prevent the formation of incombustible mixtures. When the throttle valve begins to close during the conditions mentioned above, its movement is restricted by the force of the spring in diaphragm A, in addition to the gradual increase of vacuum in diaphragm B.