Yep, I remember the TCS system. It only allowed the vacuum advance to work under very specific combinations of speed and engine temperature. The GM engineers had found that it was possible to reduce unburned hydrocarbons by retarding the timing a little, and the easiest way to do that was to prevent the vacuum advance from working in the part-throttle ranges. A speed-sensor switch and a vacuum valve kept the intake vacuum away from the advance chamber unless the speed was above a certain limit or the engine started to overheat. Then the vacuum would get switched to the advance, and it would operate and cool the engine down due to higher idle speed and fan volume, plus the earlier timing kept the combustion chambers and exhaust manifolds cooler. Some of those early emission control systems were real Rube Goldberg operations that almost guaranteed lousy gas mileage, even if the engine did run lean enough to pass federal emission requirements!
Jerry
