My peddle would actually move and get stiffer with boost engaged and go soft under vacuum. There is a valve in this hose that lets boost pressure go one way only. That valve was broken. I was probably wasting boost. The main side effect was that it would create a whistle under high boost. For the longest time I thought it was my Blitz boost gauge. 😛
Take it off and do a vacuum check on it. The manual has a page for the full procedure. The new hose is about $7 if I remember correctly.
Part # MB 892600