i'd give the car a good service before anything else. Sounds like the 100k service hasn't been done anyway. So oil, oil filter, timing belt, fuel pump, spark plugs etc. clean the injectors out like mentioned previously and see if that makes a difference. It may just be worth it to try and sell it, but if the body is in good nick, i would build around it and maybe drop a b20 into it. You could buy a b18 halfcut for a few grand and that will give you everything that needs replacing in your car now anyway. Might save you a bit in the long run if the motor has internal damage from being ridden hard for it's entire life.