1LOVE_WS6

I am getting some error mesages and I am trying to figure out what's wrong. Can anyone help? Has anyone else experience this before? The error messages are P0171, P0174, P0300, and P0300.The car is a 00' WS6. I know what the error messages mean, but I am concern about what is causing the lean fuel left bank and right bank, and the misfiring. Can anyone help, trying to save some dollars.

wrencher

iTrader: (2)

Deal with the missfire code first.
Has a tune up ever been done?
The missfiring cylinder will not burn the oxygen inside itself & the o2 detects this as= lean.

ss rally red

iTrader: (8)

How many miles on the car? Any recent mods?