Injectors normally only misfire at idle speeds when the rail pressure is at it's lowest. A lack of spark shows up as a miss under heavy load, usually in the midrange. So sounds spark related from your description. Plugs next as /\ said.
If you still get a misfire, monitor which cyl with VCDS, then replace that injector. Well, may as well do all 4 whilst you're there as it's a faff of a job.