P0171 - LS Lincoln Cars & Trucks

This is an obd2 trouble code table, it can help you understand the meaning of code. and for p0171
the possible cause:
The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor.
the possible solution:
In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure

System is running lean on Bank One. Check for a vaccum leak at the intake manifold, vacuum lines etc. verify good fuel pressure, and make sure that your O2 sensors are working properly.