Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Deceleration Control System: Description
The decel throttle control (modulator) system keeps the throttle valves slightly open during sudden deceleration to help reduce hydrocarbon and carbon monoxide emissions.
The system consists of a governor module or speed sensor, ported vacuum switch (some models), solenoid vacuum valve, throttle positioner (modulator) on throttle linkage, electrical wiring and vacuum hoses. See Figure .
Some systems also utilize a vacuum switch that notifies the module or speed sensor when the manifold vacuum is at a predetermined level. The system is electrically connected to the ignition switch and "TACH" terminal of the ignition coil.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.