I own a 2000 mustang 3.8l, and i deleted muffler but still have the cats and i just put a 90 degree angle pipe after the Y and made come out the driver side, it sounds pretty good, but it definitely ain't no v8. But here is the problem, i started it up one day and it kept idling rough. going from 500 to 800 back and forth and it felt like it was missing, i revved it up to 1600 and it stopped having the missing feeling and acted normal, could this be a back pressure problem because its just straight piped after the Y or should i check the plugs, make sure they all are firing, the reason i don't think its a plug is because its normal when i rev it or when im driving around. it also has the missing feeling if i give it a little bit of gas and the rpms stay low, the whole engine shakes.