Please help!

I've got about 130K miles on my focus and the battery light would turn on and off. So, we've replaced the battery and it that didn't work. Just got the alternator replaced and that fixed the battery light problem Now, when the car is in park or nuetral and the rpm's are reved to 3, the car stalls. Also, I had to come to a quick stop yesterday and it stalled. Any ideas?

Check for a loose vacuum hose around where you did the work.

As I've been driving my car over the last couple weeks, when I slow down the car feels like its going to stall and it has a couple times. I got it diagnosed over the weekend and they said it came back with an mass air flow sensor code. Does this sound like the problem and does anyone know how much it usually costs to get it fixed?