if its reading lean, off the top of my head it could be a few things
air leak? smoke test would be ideal.. this little smoke machine is pretty bad @ss... few techs have these at work they put out a lot of smoke which is good. they feel light duty, but they work:
Smoke Machine link on Amazon
maybe try CRC Mass Airflow cleaner, or CRC electric cleaner.. maybe aftermarket oil'd air filter contaminated the Sensor?
If no intake leak, then check fuel pressure.
If fuel pressure is good, check fuel flow... not sure what the spec is, but you can have good pressure, but low flow... like collapsed fuel line or clogged injectors.... pressure will be good up to the clog...
Another thing to check is Ethanol content.. theres some simple kits to check... if you have a lot of ethanol in the fuel, that could be a cause for running lean.
if no air leaks, good fuel, good fuel pressure, and good flow, maybe look into the tune? Before going to tuner, I would have a wide band installed and look at the readings before you go, so you can know for sure that its running lean, and when you get it back from the tuner, you can look at the same gauge, and see its fixed.
I can imagine, some will just just skip smoke testing and say yes, no air leaks and just skip over to its the tune, but when you go to the tuner, they will charge you for their time.. mine as well just do everything you can do before you go to them
side note, if you have a card style mass airlfow sensor, if the tube that its mounted in is not the exact same diameter as OEM, it will run poorly... I found that out on my l83 87.... forget which way the readings went, but it went max one way, rpms were way low.... clear adaptions, idle restored for a few seconds and then would run poorly again....
another side note, is the mass airflow sensor factory? aftermarket? wheres the mass airflow sensor.... it should be about 12" or away from throttle body if I recall correctly... to close and it gets some funky readings.
this is what I would look at if it were a car in my bay at work.
clint