1992 E36 325i Sedan, Check Engine light please help to get rid off it!

[peruvianbeamer7]

So i have a 1992 325i Sedan the car has 262000 miles and still running strong, ill be honest i've always had problems with check engine light, but finally i said i like to get the check engine light to go away so i took it to the mechanic and they replaced the oxygen sensor, relays, catalytic converter, i bought a used dme from ebay and still it wont go away, now i was told it could be a faulty mass air flow sensor. : (, can someone please give me any other suggestions how i could fix this ill appreciated thank you

[flyfishvt]

What are the codes that are making it turn on? Please tell me that mechanic scanned the car for codes before he had you spend all that money on parts and labor