I will bet money it's the spark plugs.

My car did the EXACT same thing when i had some Iridium plugs in it. Couldn't figure it out for about 3 months, till one day the car started running rough and i took it to a dealership. The spark plugs were causing it, and the next day i put in a set of NGK's and the problem was gone.


Put a new set of NGK's in there and make sure they are gapped correctly.