Deceleration Valve: Description and Operation

Fig. 89 Throttle closure system:

This system. Fig.89, is used on 1983-84 Civic 1300 with 5 speed manual transmission. This system closes the throttle valve below its idle position when vehicle is decelerated under certain conditions.
When engine speed is above 800 RPM ON 1983-84 Civic 1300 and vehicle speed is above 10 mph, clutch pedal is not depressed and vacuum switch A is On for 1984 models, the throttle control valve is activated by the control unit. Vacuum is then routed through the throttle control solenoid valve and into the throttle closer, which retracts the carburetor throttle stop screw.
On 1983-84 models, the throttle valve is then completely closed, and minimum fuel required to maintain engine firing is drawn from the slow speed fuel system. When throttle valve is closed, additional air is delivered into the intake manifold through the air valve. The control valve actuates the air valve according to carburetor insulator vacuum level.