Limp mode on skoda 130pd awx engine

I have a !.9tdi 130pd skoda superb and while driving the car, the car will go into limp mode. the aa plugged there vixen(laptop) into the car and it registered fault code P0299 which suggests turbo underboost, i have done a full service(oil, oil filter, air filter, diesel filter), just fitted new cat this morning, car didnt have any cat and problem still exists. any help? i have found on some forums that it is suggested a vacume test be done, if so, where can i do this or can i do it myself? how can i check for leaks? any faulty sensors?