I'm new to this forum, but I can't find any solid answers for the problem that I'm having. It's an 04 a4 Quattro 1.8. I was throwing a code for underboost. So I ended up replacing my diverter valve, pcv valves, n75 valve and now the turbo. And the car was pressure tested to 20psi And I'm still having the same problem. The car feels powerless and a have a flapping noise when I get into boost. Any ideas? Thanks ahead