If it stored any codes due to the unplugged MAS, clear them from memory first. If that's not it, then I'd have to go with the regulator / pump suggestion. Put a gauge on the schrader valve on the fuel rail and start it. Record the reading, then pull and plug the vacuum hose and record that reading. Shut down and see if pressure holds.
Do a search for "stalling problem". A wealth of information awaits you.
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