Engine Sputtering

So about 3 month ago my wife 2012 Malibu 4 cyl, just started idling up and
down like it was not getting fuel I barely made it home from just being at a
drive thru I would have to blame the gas pedal down the car would drive but
the 2nd I let off the gas pedal or stop th car would sputter almost to death, I
replaced the fuel pump and the car still did the same thing I took over to a
mechanic and they said the Mass Air Flow Sensor was dirty and they ran a test
on something and it failed the Ohms test they after they reset something the
Ohm read normal but I do not understand what it was, My wife car is running
alright but now the fuel gauge does not work properly we fill the tank every
couple day but fuel gauge shows only 3/4 a tank and on cold start motor
sounds like its some what sputtering till fully warmed up and smells like fuel in
the cap while idling need help please...