For starters, I would run a good FI cleaner through it..
You may well have a gunked up injector [ as you mentioned long sitting]
The o2 sensor reads the leanest cylinder , so even just one screwed up injector can cause the ECU to get Lean message ..
I would also get the part # off the EGR valve to see if it has been change to the newer one.. there was a TSB on this for sticking valve...