2003 Kia Spectra Runs poorly

Hi. I have 2 questions. How many mass air flow sensors are there in an 03 Kia Spectra? Also, for the past 2 spring/summer seasons, my car runs poorly. Sometimes it will skip or sputter when slowing down, the idle is rough and at other times when in 2nd, 3rd or 4th gear, the car will just shut down, or stall. I had a check engine light this time around (last summer I didnt) and it calls for a knock sensor and throttle position sensor. Both I replaced already last summer. What could be causing this? Kiacurse