Spark Timing Control System: Description

The Spark Timing Control (STC) system is designed to control distributor vacuum advance during rapid acceleration in order to reduce HC and NOx emissions. On 1977-78 models, the system consist of a thermal vacuum control valve, vacuum switching valve, a spark delay valve, and various connecting hose and wiring.

On 1979 models, the vacuum delay valve is installed in the vacuum line between the carburetor and the distributor on 210 and Pickup models, or throttle chamber and distributor on 280ZX and 810 models. In addition, 210 models are equipped with a thermal vacuum valve to prevent full vacuum advance when engine coolant temperature is between 64-122°F (18-50°C).