After reviewing the emission controls for that model what you suggest makes a bit more sense. The puzzling part to the equation is the controls of that era are usually regulated through vacuum temperature switches. After a certain temperature is reached the valves are usually open, or closed depending on the circuit. Is it possible that vacuum valves of that era were designed to open at one temperature yet close at another temp? I discovered too much gray information regarding the actual operation of some/all the components in the emission control system for that era.

Thanks Duke.