If turning your air speed screw does not raise vacuum well above 16" at idle, or turning it to close doesn't nearly stall your engine, you have major vac leaks. Start with plugging the line to the central locking system (if that isn't where you have your vac pump hooked up). Have you done injector seals at all? Those hoses to and from the aux air valve can be a source of vac loss if they're old/cruddy. Your aux air valve might be sticking open too. But it sounds more like a vac leak somewhere. The most overlooked leaking area is the tranny modulator line (speaking from experience at least). Mine leaked for at least 6 months before I realized the rubber on the other end of it was shot. Took rough shifting when it fell off one end to realize it.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k