This may be a silly one but if the MAF sensor is on its way out low readings, would this effect the boost pressure ie no boost above 0.5 bar.

 

Yep, but other things can also do this..
Rob

 

What other things could cause this subaru had it for a full day they said no fault codes and no idear what was causing it. The car is booked in at PE on satarday i hope they can sort it.

 

I still think it's detting (through lean mixture 'cos of dodgy MAF) enough to make the ECU drop the boost to 0.5 bar. Mine does exactly the same at the moment on a hot day (MAF OK it's just not happy with the air filter!).