My roomster went to Vw garage (small dealer)with engine problem: when I accelerate hard it really starts chugging or pulling back.  Not like it's running on 3 cylinders but like it's just no power in it when the chugging happens.  The garage  found fault and replaced all spark plugs and plug lead 1.  Since they done it it's better but if I put foot down hard it starts the chugging again!   Spoke to mechanic who plugged in fault finding gear (vcds I think) but no fault found.  Mechanic did say Po