2006. I 2006 Focus witha MAF sensor. I was running 1 step colder copper core spark plugs with a grove cut into electrode gapped ultra wide, .055" when factory spec called for .040" non adjustable iridium plug. Don't think I was running lean, I bought it new and had all mods done by 1,500 miles on engine, ran engine to 180,000 miles before sold it last year and never had an ounce of trouble. Infact the only thing that ever broke on the car in the entire 8 years I owned it was the shift tower on the back of the transmission, which wasn't bad because the clutch had not been replaced at this point and was down to the last couple thousand miles of usable life, so all it cost me extra to do was the cost of the part.