misfire between 1,500 and 2,500rpm

hi,
i have a my95 v2 sti. Its running about 300-330bhp with the usual stage 1 mods. I get a misfire between 1,500 and 2,500rpm. If i hold the accelerator between the two you can hear 'popping' in the exhaust. it happens when its cold and hot. I bought a second hand coil pack and swaped it over each cylinder one at a time, started it to see if it stopped 'popping' but had no luck. im not sure weather to spend alot of money buying new coil packs incase is not the problem. Also ive had it mapped to 1.1 bar. would the mapping cause the misfire? please help cheers

Might be Lambda sensor as your description sounds like a fueling problem. Also if you had it mapped recently it might be worth having a word with your mapper.