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.