Throttle Positioner System: Description
The throttle positioner system controls exhaust emissions during deceleration by holding the throttle plate at an above-idle position during off-throttle operation. This prevents the fuel mixture from being starved of air and helps control HC and CO emissions. The controlling unit is a throttle positioner diaphragm which is vacuum operated. On 1975-77 models, system consist of a diaphragm type vacuum actuator which is linked to carburetor throttle valve. On 1976-77 Federal 2T-C engines, throttle positioner is controlled by means of a vacuum control valve. On all other engines, actuator is controlled by a vacuum switching valve which is controlled by vehicle speed. When system is in operation, throttle is prevented from closing completely to reduce emissions during certain periods of deceleration.