2006 BMW 325 Vibrations - not running smooth

Feeling vibrations in the pedal as i accelerate - feels like engine is misfiring or somethig.. is not a smooth acceleration but kind of a puff puff puff type accelaration....completely different than a few months ago. especially in cold weather ( 20 to 40 degrees). Dealer did NOT find anything wrong with it, upon checking (at least the computer didnt report anything). Doubt the dealer drove the car cause you can tell immediately. I balanced the tires thinking is a tire issue and nothing. I tried different type of gasolines brands BP, Shell and nothing. Tried heating the car up before staring to drive and no change. Feels terrible and it is driving me nuts. I know what a smooth drive is and i am not getting that. Any feedback woudl be extremely helpful. Ty
George