Ok this is killing me! I have a 2005 F150 Fx4 5.4 that keeps throwing a p0172 code. I've replaced all spark plugs, C.O.P's, fuel injectors, Mass airflow sensor, 1 o2 sensor, checked all vac lines and there ok. Can someone please help me with this issue?

 

Causes

A code P0172 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters can 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.
There could be a fuel pressure or delivery problem

Possible Solutions

Possible solutions include:

Inspect all vacuum and PCV hoses, replace if necessary
Cleanthe MAF sensor. 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 fuel lines for cracks, leaks, or pinches
Check the fuel pressure at the fuel rail
Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)

 

P0172 code is system too rich bank 1. I would suspect an injector has failed on bank 1. 04's and 05's had some injector issues. I would follow the diagnostic procedure in the Powertrain and Emission Control shop manual.