with both these codes present boost will be limited by the ECU to protect the engine.
most likley cause of failure is 2 open circuits in the wiring between the ECU and the components identified by the fault codes.
engine harness is pretty tight in the engine loom and harness breaks are not uncommon on these vans.
undertray off, (i think the start valve is pump mounted, and used to time commence of injection) whilst MAF is next to intake air box top LH side engine bay. Circuit diagrams and a multimeter with the components disconnected and the ECU disconnected, using wire colour coding / pin numbers on ECU and components check for continuity along each wire and also for short to GND, VBatt (make sure ECU disconnected and battery disconnected).
Open circuit most likely fault.
Short to GND via block next possible.
Least probable is short to Vbatt or 5v ref voltage.
otherwise decent auto electricial who is familiar with VW engines.