Hyundai Repair: trouble codes, air flow sensor, vacuum leaks

Question
I have trouble codes PO174 & PO171 (right & left banks lean) what are the potential causes of these codes?

Answer
Since you have a lean condition on both banks, you're looking for things that could affect both banks.  Check for vacuum leaks, especially the PCV hose for holes.  Also check to make sure air cannot enter between the air flow sensor and the throttle body.  The bellows needs to have no holes in it and needs to be securely attached to the air flow sensor and the throttle body.  If all that is okay, you probably have an issue with your air flow sensor.

Please follow up with the year and model of your car.  It's possible Hyundai has issued a technical service bulletin specifically pertaining to your car.