How do I repair a p0174 obd code in my 1999 Ford Expedition?

Hello, what do you mean when you say "every component"? If you have an isolated P0174, you have a single lean code for bank 2. This means that you don'tt have a vacuum leak or a mass air flow sensor concern in your 1999 Ford Explorer because those concerns would affect both bank one and bank two together and also give you a P0171. Your concern lies specifically with the bank in question. A diagnostic tool can monitor performance of the short and long fuel trims to see what is happening as a result of the information the sensor is providing to the engine's processor. Proper testing with proper equipment and reference materials is important.