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.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.
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