1999 Chevy Prizm started running rough, misfire in # 1 and # 4 cylinders

My 1999 Chevy Prizm started running rough. I checked it with a code reader and it revealed that I had a misfire in # 1 and # 4 cylinders. I then checked the plugs and found # 1 appeared to be fouled out. I replaced all of my plugs and cleared my check engine light. I drove it and it seemed fine for a day or so. Then the problem reappeared. I added some injector cleaner that doesn't seem to be helping. I'm thinking of replacing the plug wires, but I ohmned them out and ohmned out a new set at the auto parts store and got the same readings. I got 122,000 miles on the car. Any ideas?

maybe possible the 02 sensor is bad causing rich running condition, when was it changed last?

i am having this same problem right now. it runs rough and barely makes it up hills.I changed the plugs and wires, then i had a misfire in 2 and 4 i beleve it was, so i changed the coil pack, it ran like a champ for a day now today its doing it again. is there a cam sensor on the prism or is it an o2 sensor? please help