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.
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.
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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