I'm dealing with the same thing and The past owner of mine had a K&N filter inplace and after reading some good posts here I started by switching air filters to a standard for now. Then although I had already spent a finger on a O2 sensor I took some advice and went after the MAF. Advance Auto had eletronics cleaner and MAF SENSOR CLEANER. Although the forum said I could use Electronics cleaner I spent the extra $2 for the MAF Cleaner because I've also heard that the MAF sensor is pretty salty to replace. IIcould see oil in the bottom of the sensor staw...hmmm.
I was keeping track of my milage because it went from 300 per tank down to 250 and now isn't the time for poor milage. Unfortunately I was at a half tank when I unhooked my battery to reset the CEL (not sure how to do properly) and it clear my trip milage...bummer. So I have to Start over at $2.57 a gallon to see if things have improved.
I'd appreciate any feed back and I'll try to keep you posted of the results.