my 2000 ford focus keeps stalling. It only stalls when I stop. The check engine light is on and when I took it to advanced auto they ran the code and it comes up running to lean. So they suggested I get a new 02 sensor. So I replaced that and within a week, same thing. I did come to find out that there is two 02 sensors, but I took it to a dealer anyway and they confirmed that I needed a new 02 sensor(the one i've yet to replace) so I bought an o2 sensor and had it put it. They car ran great for about 3 weeks and now the same thing has happened again, more stalling and the same code. Help?