Throttle Modulator: Description

Throttle Modulator System is used to reduce emissions during vehicle deceleration. System consists of vacuum operated throttle modulator unit on carburetor, solenoid vacuum valve and electronic engine speed sensor used on heavy duty vehicles or a spinner valve which senses vehicle speed and controls vacuum to throttle modulator on light duty vehicles. Normally an engine will emit relatively high levels of unburned hydrocarbons during (closed throttle) deceleration. Throttle modulator system overcomes this condition by maintaining a slightly greater throttle opening (high idle) during initial deceleration, which permits intake of just enough additional air/fuel mixture to promote combustion and eliminate misfire.