I work for skoda so same difference if the fault is 100% only on one cylinder then that rules out sensors, air flow meters etc as there not cylinder specific. The coil on plugs do go fault on these but if you have already done these then that is that one ruled out.

I would (if you havent already) swap plugs around and see if the fault moves. If that doesnt then swap the injectors round and see if that moves it. If you have VAG com then miss-fire recognition is on measured values 15 (cyl 1-3) and 16 (cyl 4)

Got to be one of them 2 causing the fault I recon.

HTH

Mart