What issue causes my car to stall when in reverse & hesitate and stall while accelerating from a stop light?

When I put my foot on the break, put my car in reverse then back up out of a parking spot my car hesitates, surges and stalls. Also, when I'm at a stop light for long periods of time with my foot on the break my car hesitates, surges and stalls when I accelerate. Sometimes it even surges while driving. I don't really know anything about cars. I took it to Tuffy, big mistake, where they said the problem was the mass air flow sensor, which when replaced with a new sensor, fixed nothing and the problems seem to be worsening. My car is a 2001 Ford Focus. Two problems we were thinking it could be are the fuel pump/filter or the TPS. Someone help me please!