vrs boost issues

Might also be worth  checking the hose back from the "pancake pipe" to the TIP, which is under the OSF arch, mounted to the subframe. It is a flexible hose, wrapped in a metal heat proof cloth, held on with pop fasteners. The hose is held on by circlips and runs up to the TIP between the rear of the engine and the bulkhead.

I had it become dislodged slightly once and symptoms were erratic boost and loud hissing sound , noticibly more audible when driving with the drivers window down and then booting it around 2krpm in 3rd