Having had this done on my A2 (FSi) recently it essentially involved stripping down the whole of the inlet manifold side. Before you embark on the i would double check the operating selenoid on the side of the inlet manifold and the associated rubber vacum pipes. This had failed on mine, but this only came to light after they had replaced the manifold section containing the flaps! In my case they were not carboned up, felt free however half way through the arc there was a tight spot, it was pointed out that the cross shaft was plastic that runs in bushes and on the new genuine replacement it looks an upgraded design.
The potentiometer is only replacable once the manifold section is stripped down, or it maybe possible to replace it it once the cambelt is removed, then the plastic shield and possible one of the cam drive gears (left one covers access to the potentiometer).
Its a fiddly job, one of those that i guess once you have done it, its much quicker second time, from memory the manifold section was around the £350 mark, the various vacum hoses another £15 or so, potentiometer £40, actuator around £70 and the control selonoid another £40 or so, plus the various manifold gaskets.
Personally unless the actuator arm has snaped/flaps feel tight or have a tight spot, i would try the control selenoid/vac pipes before incur major strip down costs i.e. labour.
