I have a 1995 M3 intake, track pipe, exhaust and chip. When I went to get it smogged I took everything off except the intake. I failed. I checked the spark plugs and they were brownish/red/black so i thought the car was running too rich so I changed the 02 sensor. Took it back and it still failed, but the numbers did improve. There are no fault codes comming up so what should I do guys? Could it be an air flow meter in the process of going bad?