Since unplugging the MAP sensor makes it run better, check for a vacuum leak somewhere around the intake mainfold. The leak (if there is one) is probably fairly large to cause such a problem.

try spraying the intake area with water in a squirt bottle if the engine stalls you have norrowed down where the leak is.

(of course the MAP sensor could have Adaptive Memory which would, once the MAP is disconnected, allows the computer to go to a preset MAP reading; thereby concealing the problem).

Still would like to have the fuel pressure actually read by a guage. But later for that, let me know how the search for the vacuum leak goes.