sr20. rough idle LOUD backfire

[2.0-TURBOcoupe]

89 base model coupe

redtop sr20
s14 t28
255 walbro
z32 maf (blo through)
stock fuel injectors
brand new plugs.

ok i was driving the car a couple of nights ago and it was kind of chilly out so i turned on the heat(which works great) but it was the first time i have ever used it. afterwards i puled up to a redlight and took of driving normally and the car let out one of the loudest backfires. now, during a shift or decel of RPM the car will backfire. i was driving back to my house and i fouled a plug. i replaced the plugs but its still idling rough and when i rev it up it will back fire very very loudly. checked fuel presure. cleaned iacv. throttle body. unplugged maf(no change in idle). im at a loss. the car has never given me any sort of problem before. if anyone has any suggestions let me know