Code problem with car.
 

Ok after getting my car, my check engine light had turned on and said bad maf(code I don't remember) and P0131, well I cleared the codes because the car had a brand new set of cats put on but after about 30 miles of driving it came back on but only the P0131 not the maf code. Well the dealership replaced the 02 sensor and the code came back on again(P0131) What can be causing this?