The dreaded P0491 P0492

[jljljl]

Hey guys,
So my check engine light came on and I took it in and the mechanic said and showed the error code was P0491 and p04902. I had the o2 sensor replaced. I had the dash cleared but after a while the check engine light came back on. As I did my reading about these error codes, there were some people who said that I have to replace the pump now? But there were also some that said that there was no need to replace the pump.. and to just clear the pipes?

also it started shaking at idle one time, is that in relation with the error code? and sometimes when pressed on the accelerator, it doesn't feel like its full power?
any advice would be helpful

thanks guys