I recently got my stang back running after sitting for about 3 years. After starting it i am getting a backfire through the intake. It has new plugs wires, IAC. I also used Seafoam and ran it through the fuel, crackcase, and emissions systems. But cannot get it to stop backfiring. It only does it sometimes usually when hitting the gas intially but once running it runs fine until i have to stope such as a red light or stop sign and sometimes cuts off and i have to restart.

 

timing related. either distributor timing is way far advanced, or the chain is el-junko.

 

think about it^^^^most likely if the car didn't do this before it was parked those item sitting will not have changed = not the problem......sounds like an ignition misfire, OP you say it has new wires?? when from 3 years ago or now???......have you replaced the plugs, cap and rotor yet???