My 97 neon idles ruff then stalls when stopped. I pulled the codes and it's telling me an 02 sensor is bad. I changed the upstream sensor last year. The bad upstream sensor made the car run like a plug wire was disconnected. Will a downstream sensor cause the car to have ruff idle then stall??

 

Your O2 sensor won't cause the car to do that, all the downstream sensor does is check how well your cat is working and as for the upstream one it could have just went bad again which in a lot of cases is the colprate the upstream one, try checking your plugs to see if they are fouled any( smells like gas or possibly could have oil and in that case you need new seals to prevent oil from getting in, check color as well and stay away from bosch.It could be something with your fuel delivery as well try some fuel injection cleaner, what else is it doing? do you have any back fire going on? if so then use water removal hope some of that was helpful