TSC - Transmission Controlled Vacuum Spark Advanced System
From one source.
If there is a TCS system malfunction, first connect a vacuum gauge in the hose between the solenoid valve and the distributor vacuum unit. Drive the vehicle or raise it on a frame lift and observe the vacuum gauge. If full vacuum is available in all gears, check for the following:
If no vacuum is available in any gear, check the following:
Tests for individual components are as follows
This unit may be checked simply by observing it while an assistant switches the ignition and It should extend further with the current switched on. The unit is not repairable.
Check that proper manifold vacuum is available. Connect the vacuum gauge in the line between the solenoid valve and the distributor. Apply 12 volts to the solenoid. If vacuum is still not available, the valve is defective, either mechanically or electrically. The unit is not repairable. If the valve is satisfactory, check the relay next.
The vacuum valve solenoid should be de-energized (vacuum available) with the engine cold. If it is not, ground the green/white stripe wire from the switch. If the solenoid now de-energizes, replace the switch. If the switch was satisfactory, check the transmission switch.
With the engine at normal operating temperature and the transmission in one of the no-vacuum gears, the vacuum valve solenoid should be energized (no vacuum). If not, remove and ground the switch electrical lead. If the solenoid energizes, replace the switch.