1997 Avenger ES 2.5 stalling at idle

Partsman41953

I have the above vehicle with 152,000 easy miles on it. I do all or most of the maintenance myself. I had a check engine light on and when I had the codes read I was told it was 1 of the O2 sensors, bank 2, sensor 2. I replaced the sensor and noticed it was all full of carbon. The light went out but now the car seems to stall at time at idle and I am getting poor gas mileage. Since the light has not come back on I was not sure if the codes could be read again. I read that it could be the EGR valve and ordered one but noticed it was behind the engine next to the fire wall. I would like to know if it is the EGR valve how would you go about replacing it.

Thanks