I'd pull codes from the computer and see if there any elec/electronic faults with the fuel relay, fuel injectors and fuel pumps as there are no codes for FPR= fuel pressure regulator, this would be a vaccum issue, old/dirty fuel filters aren't going to have that kind of an effect unless the system is fouled with mud from Submarine activites Off Road.
AND in addition:
Check the throttle body blade angle for air induction that it's not fully closed with the linkage or if held open by hand, TPS = throttle position sensor, voltage setting could be off or it's failing and you might as well check the IAC = idle air control sensor on the side of the throttle body. Back probaing procedures are in the Haynes Manual.
There is a Ford Racing Performance Parts "idle setting procedure" Instruction Sheet (Techline (800) FORD788) steps 1-9 on How To adjust idle by disconnecting the IAC using the throttle body idle stop screw, drilling out the mounting screw holes on a newer "plug & play" TPS so you can adjust it for voltage setting.
In the past the ideal setting was thought to be .93-.97 volts or just under 1 volt but recently posted information regarding this appears the setting should be between .55v-.75 volts.
Posted by FSB member Jermil01 recently:
Wanted to update this thread based on some TPS adjustment information I got from one of my tuning sites. This goes against the conventional wisdom of setting the TPS closer to .95 range. Thoughts??
Regarding any ECU controlled function (and idling conditions in particular), before any strategy based adjustment can be made by a computer controlled system, it must first run somewhat normally in a default and OL mode.
To do this with a FORD you must first follow a few rules.
You must keep the TPS input above the deadband area and below the "tip in" area. On a FORD this equates to below approximately 0.9V and above 0.45. Anything above 0.90V the ECU thinks the throttle is starting to open. This brings into affect possible dashpot and fuel cut strategies which can turn one grey real fast. Below approx 0.40-0.45V the system suspects an incorrect input and substitutes a default figure.
So first off, the TPS should be set to around 0.55-0.75V. You can also disconnect the IAC then disconnect the battery for 15-20 minutes, reconnect and the computer should default back to factory settings.
Inertia Switch was designed to shut off the fuel if the vehicle is in an accident or rolls over!
Good Luck ~ :thumbup