I have two things that have happened to me, giving me the symptoms you described.
Do you have a PCIIIr? If so, your code 18 could very well be your small harness grounding out somewhere. As I recall, there's 2 or 3 wires that run from the PC's main harness, to the small red connectors tucked just under and behind the left-side radiator. You can access them from the front of your bike, just behind the front lower/inner cowl. It's a big rubber bell with several other small connectors-look for the red ones. Those are your pulse gen connectors. You can totally bypass the PC's connectors, and just plug the bikes two red connectors back together like they would be from the factory. It wont have any effect on your PC's performance, unless you have special fuel mapping for each individual cylinder.
My other thought is your fuel pressure regulator. Did you check that for leakage. But I don't think that would throw any codes, so not my first guess.