Update: things get worse. I found the O2 sensor at Pep Boys, so I installed it this morning. But when I pulled the old one out, it was wet, and there was a lot of moisture in the exhaust pipe. I don't know what this means. The new sensor didn't solve the problem, and is probably fucked again. Then I drive to work. I get in the parking lot, shut the car off, and boom- the coolant expansion tank blew up. So now, I'm sitting here waiting for a tow back to the house. I FUCKING HATE THIS CAR.