2003 nissan sentra. why would all 4 plugs be gas soaked?

yes it is throwing 4 different codes:P0031 ho2 sensor; P1148 manufactures code closed loop; Po128 thermostat coolant; P0304 misfire no4 cylinder. but no misfire is present. thermostat and coolant great and working. i dont know what the closed loop would be. the car runs fine for a while then all the sudden couple days later its flooded the plugs with gas again and wont start.