Misfire codes, inconsistent ideal to powering completely off

[P0kerd0t]

Hi everyone! I am a new (used) Subaru Imprezza Owner. The person before me did lots of modifications to the car. But it's been in and out of the shop since I've gotten it. We have replaced the spark plugs,corbon air filter, ignition coils, air mass sensor, and still these issues are apparent. I have a little video of the engine hesitating, and a little part that stops spinning randomly when the engine begins to hesitate. Can I replace that part? Is that a thing people do? Please help