hi their i have a import v1 wrx and it has started to lose power as when you start the car it starts hunting from 500 to 1000 rpm and then when u begin to drive the car it lurches back and too not icreasing speed (feels lethargic) tried reading faults and nothing found also car runs very rich as when driving lots of black smoke from the exhaust any ideas please. also the checkengine light isnt illuminated