i have chanced the spark plug wires and checked the spark pugs changed the tps the iac and the coolent temp cenur in the bell i have changed the mat too. and my car still back fires between 1 and 3500 rpms but once o am over about 45 mph the back fireing stops and i get code 24 vss from the computer i even releared the computer to see if that would help and the o2 censur is new too. i think maybe a coil went bad how can i test this. and what els would cause my car to back fire i know it is becouse the car is running too rich.