Check your clamps have not fouled against the ecu loom next to the battery.
Clean the maf with electrical contact cleaner.
Disconnected the battery and press the brake to drain power to the ecu. Reconnect start it an let it idle for 10 minutes. Drive gently for next day.
Check all boost related hoses to make sure they are tight but not over tight.
Check the small bov line to make sure it has not rubbed through against the bonnet.
Check bov spring tension is correct and not too loose.
Change back to stock bov to see if that fixes it.
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MY16 WRX STi Crystal White Pearl
-= Rally Armour Flaps - 2XS Muffler Delete =-
FG FPV F6 MKII Vixen - SOLD
-= Bluepower SRI - ID1000 Injectors - Venom Cat - XCAL3 - ProcessWest Stg2 Intercooler - 359 RWKW=-
CX9 Grand Touring Stormy Blue
-= The rolling armchair =-
6 MPS Velocity Red - SOLD
-=Cat Back Exhaust - Pirelli PZero=-
3 MPS Aurora Blue - SOLD
-=PG SRI - PG Inlet - ETS TMIC - GFB Hybrid BOV - Best Mufflers DP - Eibach Pro - AccessPort STG2 - Autotech HPFP - ITV22 - Michelin PSS=-