i do have a new air filter. band spaking new fujita....i have a A.E.M cold air intake....the sound has gotten worse it now sounds like a leak...after 3x rpm's the sound goes away, but any thing below that it sound nasty.... back fire's happen only on 1st and 2nd gear. my high flow cat is from werks 3", so im thinking of getting a magna flow 3" dual exhaust..??? oh and yes it did throw a bad code but it has gone away....FOR NOW.