Likely 02 sensors or a strange fuel control problem. With one side running rich and the other lean, that's pretty strange.
Bob will probably have a more detailed response. It's not likely to be the MAF, as it affects both sides equally and in the same direction generally. It can be O2 sensors, injectors, PCM, ignition and so on that cause that. If you're not getting misfire codes, that's probably pointing to the 02 sensors I think.