OBD codes 0171 0174

I hate to say it but a lean condition is not normally caused by the o2 sensors, they normally fail to the rich side not lean. If you have cracked vaccum lines then that is probably your problem. This is the situation, your cars sensors tell the computer how much air is being taken in and schedules the fuel based on that information. Now take a cracked vaccum line will have on that, it is able to ingest air that is not being metered by the sensors so that is why your car is running lean and are getting the codes. I would check all your vaccum lines and replace any that are questionable or excessively hard(don't mistake emission lines for vacuum lines) emission line is hard plastic). Hope it helps.

Gary