Check Engine Light, Runnign Lean

[84LX89GT]

The things i'd look at, as mentioned, is the MAF sensor which the barometric pressure reading and actual airflow calculations are made by. Using a residueless spray like brake clean or even better is electrical contact cleaner should clean it out. You can usually tell when it's contaminated because it will be sooty, or black (most times).
I'd use brake clean and spray around your engine while it's running, if you hear a change in how it runs then you have a leak in that area you have to find.
Also, putting 02 sensors farther downstream will reduce their reading ability since they have to be at their operating temperature to read properly. The 02 heaters only stay on for a few minutes at startup, the rest is done by the exhaust heat.
Check your fuel pressure with and without the vacuum line on the fuel pressure regulator to determine if that's a possible problem. With it connected i believe it should be *around* 32-35 psi, with it disconnected 38-40 psi i believe (numbers off the top of my head). You should also drive it and see under load if fuel pressure drops, you may have a restricted fuel filter.
Does your car ping at all under any condition, that could give you a clue as to what's happening.
Good luck,