I would just get the o2 sensor andclean the k&n (if it looks dirty). Mafs usually cause lean conditions more times than rich and will cause the car to bog down off the line (one single studder with an audible that I can really discribe) or it will not allow the car to start sometimes after some rough rounning and sputting. Most likely the o2 sensor is going bad and just hasn't kicked acel yet.