could be either
could be a multitude of the sensors. N75's can cause boost problems also. O2 sesors that are on there way out cause the car to in to limp 2. I had a guy last week that had taken out a fuse mistakenly was the engine managment fuse an he thort it was the heated seats 1.
low and behold put the fuse back in and hey presto!!
vag com definatly the way forward.
traumapat is right with wo t he said about software. its very rare for a map itself to cause problems on its own, although if the cars over boosting bcoz of the way the maps written then its is possible, but more likely to be a sensor of somesort.