I need help with my car my check engine light keeps coming off and on. When running a diagnostic it says the car is running lean code po171 and po1101 . I have changed the mass air flow sensor twice thinking the new part might have been faulty. The car also began running ruff during idling so I changed Vapor canister purge valve. When diagnostic came up with code po496. The po1101 and po171 I can not seem to find the cause and don't want to keep buying parts guessing what it is. If someone could help my dad lives far away so I don't have his help and there is only so much he can do over the phone.