Is the car still running on a big red pod filter (aem filter)? Tom did have the similar issue, it was the maf. Maybe u live in dusty area, and maf and filter needs a refresh? Next time u come to perth, I can give u some aem filter cleaner, or u can use the k&n one.

Also check ur spark plug as Jezza said.

using the Perth-WRX mobile app

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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