97 import wrx, totally standard

last few days, just now and then it does not give me full boost

1/2 bar compared to over 1 before

at about 4 or 5 thousand revs turbo seems to decide not to give me anymore, can still hear the whistle but it doesnt build full pressure, can hear a raspy rattly sound

then, 10 minutes later back to normal, full boost and flys like a legend

whats going on ? any ideas on what to look for first ?

THANKS TO ANYONE THAT HELPS

 

split pipe
dodgy maf or o2 sensor

start with the pipework

 

dirty boost control solenoid?

 

see thread today "boost boost boost"

try a MBC