Engine Performance problem
1990 Buick Skylark 6 cyl Front Wheel Drive 90000 miles

I have a 1990 buick 3.3, and it started to have problems on acceleration, as in passing some one, as it reached higher speeds it would begin to stumble. If I let up off the throttle a little it would smooth out and still accelerate. Fuel pressure was low so I changed the fuel pump, strainer and filter. Inside the tank looked nice and clean. Now I've got a trouble code for a mass air flow sensor,low air flow indicated, with the air cleaner on or off. If the car starts at all, with it idling, when you attempt to accelerate, the engine just sucks air and won't accelerate but will return to idle once you let off the gas pedal. Within the last 6 months I've also replaced the Fuel Pressure Regulator. Got any ideas on what might be wrong, anybody?