The TCS vacuum solenoid opened in last gear, also with engine cold or too hot.
The solenoid is controlled by a switch, on M/T linkage or on the A/T valve body and the temperature sending unit on intake.
This makes for NO vacuum advance at idle speed at normal engine operating temperature.
The TCS system has NOTHING to do with the carburetor throttle angle.
What the TCS does, is controling the ignition vacuum advance under various driving conditions.
The purpose of reduced amounts of timing at idle speeds via the TCS-system is heating the cylinder heads to reduce the amounts of HC out the exhaust.
The TCS-system were used on all 1970-74 Pontiac engines exc. 1971 455H.O.
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