I do not know anything about 5S cars, but is there such a thing on the carb end that pumps up the throttle when the A/C is turned on? There is such a thing on some big block 1970 Mopar stuff with factory A/C. A shot in the dark .....
Otherwise, I also know for a fact that my 1966 Jag has a vacuum resevoir for just such an occasion. I found a resevoir for cruise control for a GM vehicle -- same idea. Here it is:
Vacuum Resevoir
Do all of the easy stuff first -- then go on to the crazy stuff that I have listed here.
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