Similar issue, intermittent no-response from throttle. Key on and check throttle function, I could hear the throttle motor cycling with the accelerator pot. I also was missing a vacuum cap, and had throttle response briefly once I replaced the cap. However, now the engine would rev up, but not hold RPM; gradually the engine dropped revs and died. Swapped the MAP sensor (actually just a vacuum sensor in this application) and everything cleared up.

Thanks for posting the fix on this, just had the exact same thing happen, and sure enough it was missing a plug on a vacuum line!

Nevermind found the problem a vacuum plug fell off the carb cant find a vacuum line that went to it so we plugged it runs like a dream