It sounds like it might be the IPR then. It only has the stumble when the engine is cold or cool. It runs fine when it is warmed up.
Next question, what is the IPR? What does it do? Where is it located? How do I go about replacing it?
Thanks
IPR is the Injector Pressure Regulator. It is located on the HPOP at the forward end of the engine valley, sort of underneath the fuel filter housing.
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It is basically a solenoid actuated relief valve that controls the amount of HPOP output pressure by variing the amount of oil pressure being relieved.
It is removed by 1st disconnecting the solenoid wire connector and then removing the sheet metal nut. The solenoid will then slide off the IPR shaft towards the rear. Then you need to remove the IPR body from the HPOP. But be advised, once you do that, oil will come out of the HPOP reservoir at a rate great enough to make a big mess. You can either try to suck the oil out thru the little filler port at the top of the HPOP reservoir or catch as much oil as you can with rags. You will need a deep well socket to get the IPR out. I don't know what size. But what I used is the same socket I use to get the front axle shaft nut off a front wheel drive GM. It's a bit deeper than a regular deep well socket, which you'll need to clear the IPR shaft. When you re-install the IPR, you will need to refill the oil in the HPOP reservoir. There is a small filler plug with a allen wrench slot atop the HPOP reservoir where you do the refilling.
The IPR is replaceable as a unit, or rebuildable with a service kit available from a lot of places Ford, IH or many of the sponsoring vendors around here.
