Peugeot 4007 Boost Pressure Fault

I had something similar with my 4007. Same symptoms. Have you checked for any vacuum leaks? A faulty vacuum switching valve can cause compressor surge, leading to turbo lag and pressure drops. Might be worth a look before diving into more complicated things like the pressure sensor.

Vacuum leaks... where exactly should I be looking?

Honestly, it's tricky to pinpoint without proper equipment. But the hoses around the turbo and the vacuum switching valve itself are good starting points. If you're not comfortable poking around, a workshop will probably find it quickly. Could be a split hose or the valve failing internally.

Thanks for the tip! It was indeed the vacuum switching valve – cost me 140€ to get it sorted. Much appreciated!