gt running on 3 cylinders :( on idle and up to 3000rpm

[I_DUB_THEE]

hi i'm new to the whole polo thing and i've got myself a mk3 gt, was wondering if anyone had any previous experience that could shed some light on my little beast. on idle the cars revs will fluctuate to the point that it almost cuts out and it will run on 3 up to about 3000rpm which really does my tree in when driving through town as it sucks in juice, it has an ecu chip in it which i think is the first model chip produced which i didnt fit and it has a pipercross induction kit, would this have any effect?
i have put injector cleaner in the petrol and it has had new plugs and ht leads, any ideas? please?
ol.

[grantvw]

hi un plug the throttle position sensor on the side of the throttle body and it should stay at 1500rpm while stood if it does it should be the throttle positioning sensor that needs replacing i've got the same problem at the mo the sensor is about £30 from vag parts

[I_DUB_THEE]

not atm obviously its dark. and apparently theirs a man on the run with a gun in these parts