Ford Repair: engin light came on, advanced auto parts, 2004 ford expedition eddie bauer

Question
I have a 2004 Ford Expedition Eddie Bauer 5.4 V8. The service engine light came on. I went to Advanced auto parts and they hooked up the helpful device under the dash. It said bank 1 and bank 2 system to lean PO 171 and PO 174. I put some fuel injector cleaner in the gas tank. I will be taking the vehicle in soon for a service to change the fuel filter. That was last done at about 100 thousand mile I now have 155 thousand. Where do I go to find out what the PO171 and PO174 mean in more detail? Am I going about this in the correct way to solve the problem. The service engine light has not come back on. I have only driven about 30 miles.

Answer
i need to know what engine is in this vehicle. if it is a 5.4 litre engine. you either have a cracked vacuum line to the E.G.R. valve or if you remove where the air filter goes in, you'll notice that there is an old weather strip that hAS DETERIORATED over time. replace it with any old weatherstrip purchased at a home depot