Ok heres the deal. After replacing the o ring on my hard water pipe that goes into my water pump, I replaced my alternator with a new one. No more leaks or anything now, but when I get into the gas, its like theres somethng stuffed in the intake or exhaust. Either one. There is nothing in my intake or any other pipes or lines. I dont know if theres a leak or what the hell it is. Any ideas? My car ran perfect before I replaced the o-ring and the alternator. Pleez help

another note: this is only doing this at lower rpm's like in first when I'm first taking off. If I ease into it slowly, it will run fine( I guess). If i punch it it sputters and backfires.
I replaced my j-pipe gasket and finally tightened it up so Im not leaking anymore.