fuel consumption

Does anyone have any suggestions on why my mpg seems to be dropping recently? When I first bought the car in January there was a problem with the boost controller (the check engine light came on) which affected the power to the turbo and used the fuel like crazy. The dealership fixed it by replacing the valve/controller and it ran great until a week ago. The car seems to be surging in 3rd and 4th gear and using more fuel, but the check engine light has not come on yet. I am taking it in for oil change, etc, and they are going to check out what the problem might be, but just for kicks does anyone have any ideas?

Sounds like the Mass Air Flow sensor may be going dead(common problem)--does it run up to about 2800-3000 RPM and "Stall out"

sort of, I guess by "stall out" you mean the turbo surges.... if so it stalls out between 2400 and 2800 rpm, right where the turbo is supposed to be kicking in.