Check engine light on BMW 93, 525i, pls help

[viet nguyen]

My car has check engine light on. I took car to BMW dealer and found 175800 codes stored in DME .50 interrogated fault memory, found fault for O2 sensor stored and for O2 sensor control. I also found two hoses from crankcase vent missing, another hose gummy and part torn off. They told me this problem causes and unmeter air leak causing the O2 sensor control fault, mixture too lean.
I fixed the above problems but the engine light did not go off. Therefore, I took my car back to the dealer and they found 176241 faults for control limit reached too rich and O2 shorted to B-.1.0 interrogated fault memory. Checked O2 and O2 heater, checked wiring from O2 relay to O2 and relay to DMW. All wiring is ok. They recommend me to check fuel PSI mass airflow sensor and check intake for leaks. Then I took my car to auto repair. They checked all of them and everything is ok.
Three days ago I replaced air filter but it does not work at all. Mileage per gallon (MPG) is very low, about 13-14 MPG.
Please let me know what possible causes and what next steps I should take.
Thanks for any help.

[viet nguyen]

hello

[Aston_Jag_Tech]

Best decision is to let BMW take care of it, they know exatcly how to fix it with the exatc knowledge and tools.

Scott