Re: 00 civic si missfire and CEL
o2 sensor heater wire should have absolutely nothing to do with the misfire... check the wiring/harness leading back to the first sensor. the first reply has the right idea.
Misfire is more than likely an electrical ignition issue. my guess is that the CEL light is a misfire code. Could be so much more info behind that CEL light, theres probably more than one and my guess is that your fancy little paperclip doesnt tell you that. If you by chance happen to be around the south wisconsin area, you can come over and i'll read it. My scan tool does everything.
Otherwise, go to an advanced auto parts and have them read it. or a dealer, again just to read it. plugs and wires could be your fix, who knows.