Spark Control System (Tercel)

To help reduce hydrocarbon (HC) and oxides of nitrogen (NOx) emissions, this system delays vacuum advance when engine is hot. This lowers maximum combustion temperature. The system also improves cold engine performance by advancing the timing when the engine is cold. When engine warms, vacuum advance is provided at idle only.

A temperature sensitive Bimetallic Vacuum Switching Valve (BVSV) controls the vacuum signal to the distributor sub-vacuum advance diaphragm. On vehicle equipped with manual transmissions, a second BVSV controls distributor primary vacuum advance diaphragm.