Check engine light came on and it comes up as not getting enough air

I don't remember the code when I bought the van the guy told me it's the o2 sensor so I had it plugged in and it came up that it's not getting enough air. I'm gonna do tune up and change air filter just don't know what would cause this it's a 4.3 liter v6

Thanks I'm going today and have it plugged in again and getting it printed would you like for the codes or could I just look it up and it tells me

ok,post code(s) here....no code will tell you exactly what is wrong from an OBDll code reader,only possible causes....

Thanks I'm going again today and having it plugged in I shoot the numbers to you