So after a while suspecting my s3 of being a bit underpowered i replaced the vac lines etc with silicone, replaced the dv and put a silicone TIP on. Didnt make a whole lot of difference.
When i unplugged the N75 the car ran nice and smooth but was of course underpowered.
When i unplugged the MAF the car ran at its best so far. I bought a generic MAF and put it in and quickly realised that it was pure ****e. The idle was lumpy and the the drive was undriveable.
I got my hands on a replacement bosch one now and it seems to be good BUT...The delivery of boost without the MAF plugged in was still much better, with it plugged in there are still occasional moments of hesitation combined with lots of whoosh and no go..it does sound lie an intermittent boost leak.