Are they IRIWAY7 plugs? As these are a raceplug - So i am told by my tuner from his NGK supplier.
If so take them out and get some a lower heat range plug, the RB25DET engine is suppose to have a 5 in there, a 7 is too cold, so its going to foul and misfire as the plug isn't getting hot enough to burn the carbon build up off. So put in a 5 or a 6, when i did my mods back in October, i bought those plugs...they lasted about 1-1.5months and started to misfire - car sounded like a WRX. I took it back to my tuner and he put in some heat range 6 plugs that have been gaped to 0.8mm - i think. So far the car has been fine, been about 2-3 weeks so far.
EDIT: Either way, 7 is too cold, take them out and put a 5 or 6 in.