thought I'd throw this one out there. My S4 is restricting boost under heavy load. If the accelerator is gradually pressed she boosts perfect and acceleration is rapid, however, if the accelerator is fully depressed, the car will start to boost and then suddenly cut all boost. I think the fault code is pressure control? cannot remember what VAG-COM said but possibly a vacuum leak somewhere?
Car is at RSD being looked at but thought I'd throw it out there for any ideas.?