whats up all!!! just advanced my timing to 15 degres (dont worry i have been running 93 octain since i bought he car hah)but anyways since i advanced it my car has been missing/sputiring but only if the car is in nutral and u holdthe rpms at about 3000 to 4500 it goes um berrrrrrrrrrrrrrrr bu bu bu brrrrrrrr bu bu .. you get what im saying ha. my step dad who is a mechanic said its not the spark plugs missing so what could it be??? anything to do with adv timing????? is it normal???Thank for any help..