The O2 sensor reports to the computer, probably not the issue.
Start with the easy cheap stuff like:
How is the fuel pressure
When was the last time you changed the fuel filter
Look for vac leaks (spraying starter fluid won't do it, the computer is too fast) but you
may see an rpm change or short term fuel trim change on the scanner.
Do you have any exhaust leaks, that too can make it read lean.
Did you check for pending codes
Check the entire PCV system for soft or cracked hoses
Did you check the misfire monitor with the scanner
The hunt is on!
