Throttle Control System

The throttle controller functions as a dashpot and a cranking opener. The dashpot is provided to control hydrocarbon emissions during deceleration or during shifting gears by preventing the throttle valve from shutting rapidly.
When engine is at idle, intake manifold vacuum is applied on the diaphragm of the throttle controller through the orifice of the dashpot check valve and pulls up the diaphragm rod, so that the throttle valve is in the idle position.
After vehicle starts to run, and as intake manifold vacuum decreases, the vacuum stored in the throttle controller leaks through the dashpot check valve and throttle controller ceases to pull diaphragm rod.
When vehicle decelerates or when manual transmission is shifted, the throttle valve closes rapidly to the position where the throttle valve lever is stopped with the diaphragm rod, and gradually returns to idle position as high intake manifold vacuum slowly reaches the diaphragm of the throttle controller through the orifice of the dashpot check valve.
During cranking with the starter, the spring in the throttle controller pushes the throttle valve open a certain amount for assisting engine starting.