Car idles at around 400RPMs when warm?

I had the same car, same year, sounds like the same problem. Does it feel like it's going to stall when you stop? Mine was the EGR valve. You're 02 sensor will improve your gas milage, but will not make your car run bad. I had my convertor cut off, meaning no 02 sensors, and it ran just fine. Good luck, and you have a good little car. Mine gave me little problems until it got totalled in October.