I'm going nuts trying to figure this one out. Every once in a while my 305 tbi will backfire through the throttle body when I first take off from a standing start. I have a new coil, wires, cap and rotor. I was thinking that maybe the EGR valve wasn't working causeing a lean situation and the backfire. I have also checked for vaccum leaks and not found any. Sure could use some help with this. Thanks

 

i had the same type problem.. first of all you have to make sure it is a "back fire" i dont remember which is which but an after fire is also used.. one is out of the exaust and the other is in your tbi..
mine was in the tbi so if yours is as well.. then i offer this bit of advise.. first of all when you put the new wirs in did you use the little plastic things that hold them apart? that was my problem.. i thought it was stupid but make sure no wires are touching each other. when the spar connects it fires into the wrong cylinder at the wrong time when the wrong valve is open causing my little problem.. so make sure all of your wires are seperated from each other.. also make sure your coil wire isnt touching anything especially the air cleaner or dist. hope any of this helps. it helped me