2005 Pontiac GTO P0171 and P0174

Since I bought this car back in August I have been getting a MIL and these are the codes. The light will come on and go off every few days to every few weeks. A friend of mine did a smoke test to check for vacuum leaks and found two. He fixed them and no luck. I have also cleaned the MAF and no luck there either.
Recently I had a rough idle and with a scan tool I found out the drivers side o2 sensor was acting up. I changed it and the idle went back to normal and I thought I cleared up the codes, but they came back a week later. Where else can I look to fix this problem? Also, can I be causing damage while this is going unfixed? If this helps, I believe the light only comes on during idle. It is always bank 1 & 2. Thanks in advance.
Keith Anyon