backfire in intake once in a while

i just bought this 92 astro and it ran like garbage it smoked alot but i changed the plugs, wires, distributor and rotor, pcv, new air filter oil change and it runs real smooth now but every once in a while if i give it alot of gas in park it will backfire in the intake. it only happens every once in a while not often. what else can i check? egr? coolant temp sensor? the gauge doesn't even move when it is running, fuel pressure regulator?? i havent changed the fuel filter yet. it doesn't smoke as much maybe just a little. when i got it alot of water came out of the exhaust and alot of carbon came out also but i don't see that no more. appreciate your help thanks.

oh and i forgot to say it's a 4.3 "Z" and the exhaust does smell like fuel somewhat

you still have an ignition problem, probably a bad spark plug wire or connection or a bad coil. if those check out look for worn distributer bearings.