Suburus are not bad or weak at all most problems stem from running Jap maps designed for 100 Ron fuel on our 97 or 95 Ron. I have had 2 my current one a twinscroll jdm and are very strong I would defo get it checked out as any engine run outside what it's mapped for is looking for trouble. Although the maf does measure air entering engine and adds fuel to suit but a larger turbo would draw more air and if the maf scaling can't measure the airflow correctly it will calculate fuel incorrect and probably run lean with disastrous results. Any car run outside of it's map tables is on borrowed time