If the F 150 is a computer controlled model, check the computer codes. A bad sensor can confuse the computer, causing it to mix the air/ fuel ratio to run lean. Also check the egr valve to insure that is not clogged.
sounds like the motor is running lean, not enough fuel.
system to lean bank one 02 sensor ?
Perhaps a clogged fuel filter.
check the maf sensor
Check your Plugs and coils
all controlled by computer,see dealer for diagnostics
Could be sucking air into intake.
Trouble code P2195 means: Lack of HO2S-11 Switching, Sensor Indicates Lean
Trouble code P0171 means: Fuel System Too Lean (Cylinder Bank 1)
If you are getting a Lean code then it is probably being caused by the intake plennum gaskets. This is a common problem on the Windstar. The fix is relatively easy.
The fuel mixture is wrong in both banks. Improper fuel to air mixture is called lean. Running a code test on the vehicle may show what could be causing the problem.
running lean. too many possibilities to narrow down