Mass Air Flow Sensor

I bought my car used, its a 2004 Toyota Celica GTS and I had the code P0171 on the dash, so I started first by replacing the o2 sensors. Drove the car still had the code after I erased it and then I replaced the mass air flow sensor and then when I drove and started slowing down to come to a stop, my car would idle low and then sometimes stall. So, I am thinking it could be my mass air flow sensor being faulty. Would this cause the car to idle low and stall? Like I said my vehicle never stalled till I replaced the mass air flow sensor, this is why I would think it would be my problem.