What I would do:
Hook up a scan tool at look at your sensor voltage. It should be bouncing between ~0 and 1v. If it's not, tell me what it's doing.
If it's stuck around 0v, then it's lean. If it's around 1v, then it's rich.
Also check your short and long term fuel trims.
And to add to the diagnostic info given:
- An exhaust leak can cause an erroneous lean condition
- A leaking injector can cause an erroneous rich condition
- Don't rule out spark plugs / coil packs. Those can do some funny things
- Check your misfire indicators on all cylinders, paying mind to bank 1 (cylinders 1,3,5,7, driver's side). Issues with injectors / vacuum leaks / exhaust leaks can show up as abnormalities here, without necessarily being high enough to trigger a code