Dont replace, upgrade
So my check engine light was on for a while and i finally decided to get it read and it was P0304 (Missfire No. 4) and the primary O2. I did all new plugs and coils and new O2 and the light stayed off for about a week until i raced some guy then the light was back on when i started my car later that day. It keeps staying off for a few days at a time but then it turns back on for about a day then back off. Yesterday it turned back on after doing a 1st gear pull so the next day I got it read and it was the P0304 again but it shut off after turning my car back on later on the same day i got it read. The exhaust pops when at idle but the rpms dont jump or anything and kinda gargles when I down shift (i also have a header, 3in exhaust, and SRI). My next move is to move the coil from 4 to 2 and see if the missfire jumps and if it doesn't jump then I'm gonna get a compression with downdraft test done. I was just wondering if anyone knows what might be causing this or knows a fix. Thanks for any help.