IIRC, you would only add an O2 sensor for the auto tune on a PCV. I thought that was a second sensor (like you would have one on each header and the y-pipe on a car), but my stock exhaust doesn't have one at all.

Have you recently messed with where or how the throttle cables are routed? Or have you zip tied something and looped the tie around the throttle cables? They could be getting bound up.

I know from experience that this could definitely screw things up :(

Me too.

Whad year 650r? Its got to have a stock O2 sensor; its fuel injected.

Nope, nope, and nope. Only thing I can see is that it's from bad gas or city driving. I changed the plugs and they're burning just right. My service manual clearly says (europe models) everywhere the Oxygen Sensor is mentioned. The service code (FI Light) tables state the output voltage and the blink code for a bad sensor. Not getting an FI light. Plus, the diagrams show it on the top left of the muffler toward the front. Nothing there on my '07- must be an open-loop system. Now, '09 and up may have it on US models, I don't know.