I've got a '55 plate GTI which I picked up in September. Having come from a mapped 140 tdi I thought the performance was ok but nothing to shout about, love the smooth petrol engine though !
Anyway I thought I'd check the PCV and DV as they're prone to failure. When I removed the dipstick the engine hunted and almost stalled so I thought all was ok, however when I checked the PCV you could blow through the pipe from the manifold to the valve so it was replaced. Noticed straight away that the idle was smoother and it picked up a lot quicker.
Then for the DV. It must have been the original B revision (never heard of a B, though they were all C) and was full of holes so I picked up a G revision from the dealers and fitted that.
What a difference now ! HUGE improvement in power, pickup and mid range grunt, I really can't believe the diffence. The shove in the back is what I missed from the tdi but now I've got it in the GTI plus an instant 3-4MPG improvement on the same route. Well worth checking, here's what I got if you're interested
DV = 06F145710G £32.37 + VAT
PCV = 06F129101N £30.77 + VAT
Worth every penny !