[mark '87 930]

i went on a little trip this weekend, and on my way up to my destination, i noticed two things:
1) the car was getting HORRIBLE gas mileage.. like 8-9 mpg on the highway whereas I used to get ~25..
2) When I hammered the gas in higher gears the car was not moving, in fact was pretty much feeling like it was stalling... then i noticed in my mirror that clouds of very black smoke were coming out the muffler

When I got up there, I disconnected my o2 sensor, and everything from there forward was fine.. i hit the throttle and she pulls like she should...

So....as some of you may have read, I've very recently replaced my headers and put on a set of GHL w/heat. In doing that, I've had to take off the o2 sensor from the stock exhaust and install in the new one. I had to heat it up red for it to even budge... did I ruin it?