i had the exact same problem on my s2, i had a fcuked actuator and my lower boost hose that goes from the induction kit to the turbo was collapsing unser boost so i put a set of samcos on and a new actuator then had it set up and now it runs sweet as a nut! get it inot the tuners mate , its probably the fueling as mine was using 30% more than it shouldve been!