Engine Problem
 

Hello, I am new here, I just bought my 08 avalanche 4x2, and I it has the check engine light on, in my scanner shows P175, too rich bank 2, the engine has a little vibration, it goes on and off, engine temp a littler higher than the middle line, rpms goes from 600 to 900, all this happens at iddle, once you are driving nothing happens. The mecanics scanner didnt show any problem.
Thanks for your help