[fastassfocus]

today my car just started backfiring really bad when i start to accelerate like its running really rich. but after i drive it for about ten miniutes it gets a lot better but it still does it a little bit. could this be an 02 sensor going bad? And also which one is the one that usually goes bad? the first one or the second one? could this have anything to do with new race header?
thanks
ryan