Buying a 323 sp20 and while test driving it when I’m in second or third giving it a bit the car has this shake it like happens twice one after the other, kinda feels like a misfire but don’t wanna jump into conclusions, clutch feels good. But I told the guy to check it out and he found the code P0421, which is cat or o2 sensor, could that have anything to do with the ‘misfire’