1996 Toyota Camry

I am working on a 1996 Toyota Camry with a 3.0L V6 (1MZ-FE). After the Check Engine Light came on and there was a noticeable difference in the way the vehicle runs, especially on start up, I pulled the codes to find PO 302 306 171 100 and 110 stored. I began troubleshooting by replacing the spark plugs, clearing the codes and test driving the vehicle. There was a noticeable difference in the way the vehicle ran, however, the Check Engine Light tripped again. I pulled the codes again and came up with PO 171. I ended up installing a used MAF sensor I had on hand, cleared the code, test drove the vehicle and again had the Check Engine Light come on. I pulled the codes again and came up with PO 171, system to lean bank 1. I am not sure what the next step in the diagnosis process would be? Any help would be greatly appreciated. On a side note I noticed a small amount of oil in the intake hose between the MAF sensor and throttle body. Any ideas? Thank you in advance.