hi all, i recently changed the exhaust on my 2001 buyeye wagon wrx as i was told my awful rattling was my cat! i changed the system from turbo back to a japspeed sports catr system, sounds great rattle still there! rattling was coming from up pipe due to the lack of funds i removed the up pipe and cut the cat out welded back together, car still passes emissions and rattling stop great, but now its caused the car to misfire/back fire when i driving spirited!! does it sound like i need a remap if so how much am i looking to pay for this? cheers