Throttle Return Control System: Description

A Throttle Return Control (TRC) system is used on all Heavy Duty emission models. On deceleration, TRC system opens throttle slightly to reduce hydrocarbon emissions. The 1975-78 system consists of a vacuum control valve and a throttle lever actuator. The 1979 system consists of a throttle lever actuator, a solenoid vacuum control valve and an electronic speed sensor.