I just bought a 2001 insight with 66200 miles on it, drove it home (450 miles) and everything seemed to be fine. I was on another 100 mile trip the next day, I had noticed that between 1800 and 2200 RPMs the car would studder a bit. On my way home the CEL came on I checked the codes and it registered cylinder 1, 2 and 3 all misfiring. I just ordered new plugs today to see if that would fix the problem but then I also read that it could be the O2 sensor. What are the chances of that being the case? if none of these fix it what could it be?