P300 Random Misfire

[TjXiong]

Car: 1997 Eclipse GST Spyder

I recently been having a cel (reads p300) random misfire and everytime when I go WOT the car will misfire and studder. I first bought new wires and the car no longer misfire; a week or so after the car acts up again. Now I replaced the plugs with ngk iridum gapped at .28 with the new plugs and everything runs great but the cel keeps on coming back and forth --what could be the problem? I ve been searching and been reading all these possible problem; im stuck.

MODS - B16g - 550cc -- evo 3 o2 housing -- custom exhaust -- safc --injen intake -- blitz bov -- hallman mbc -- boost gauge -- air/fuel --walbro 255 -- this all i can remember but will update this as when i get home.

Thanks.