i had a problem a bit the same with my old one. Just had no go what it was on mine was the air flow meter there is a little sensor that hangs down and it gets covered in shit so i just blasted it with carb cleaner and just watched the shit drop off . After that it run fine. That was 2 years ago and it still runs good now with 150k on the clock. If its the cat which im shore there is only one of then i have a spare second hand one. But carb cleaner is cheaper lol.