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.
Spark Control System
This system helps reduce oxides of nitrogen (NOx) and hydrocarbon (HC) emissions by delaying vacuum advance and lowering maximum combustion temperature. System typically consists of a spark delay valve, vacuum switching valves, metered orifices, and connecting vacuum hoses.
The 1978 spark control system is operated by vacuum from advance port on carburetor or through EGR port (2F engine only). On 1979 Cressida, Corolla 1200 and Supra, the system also helps improve cold engine performance by advancing timing when engine is cold.
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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.