engine idles rough or stalls at idle

What is your question?

problem has just started. obdII memo scanner shows codes po156,po161 and po171. these are bank 2 sensor 2 codes with the exception of the 171 code. is the right side of engine,from drivers seat bank 2 and the rear sensor, sensor 2. Also can the catalytic converter be be tested to see if it is operating properly.i have replaced the o2 on the right exhaust rear sensor,about a year ago