Do u have boost gauge in ur car? If so, what's the reading now? If not maybe try spray some water on ur intake system, ie air box, turbo inlet, and intercooler, if there is leak, ur car will run rough. Might just be hose clamp on the turbo came loose?

Edit: dont spray too much though.

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport