I've been driving around with my scanner hooked up and watching sensor 2 under different conditions. I thought maybe it wasn't heated enough the first time around. But it still isn't acting like you say. It idles right around .450, and seems pretty numb to change unless I really stomp on the throttle and suddenly close it.
So what does burning coolant for so long mess with? The cat? The sensor? Both? I'm too poor for a new cat so I'm hoping it's just the sensor, but how will I know? I take it it's somewhere behind the cat? I've never noticed it in my time under the car.
Also, if it is the sensor, why the second and not the first?