On my 02, I have a problem where the engine sputters, runs like crap and has no power from when the coolant temp is roughly 110-168 degrees. During that time, the fuel pressure dips slightly before coming back up. The problem also depends on the outside air temp. When it is below 65, I don't have an issue. The hotter it is outside, the greater the problem. Truck has around 105k on it, and the problem only exists on cold starts. The fuel pump has been replaced with a new Motorcraft, same with the filter.

 

Can you scan it and check what the computer thinks the ambient temperature and coolant temperature is?

A cheap Bluetooth OBD-II reader from Amazon and a free app on an Android smartphone will do this if you don't have something already.

Not sure about the fuel pressure though, maybe regulator? If you disconnect the fuel pressure regulator vacuum hose at idle, does the pressure increase from around 28-30lbs to 38-40 lbs?

 

Faulty spark plug coil pack?

Edmo

 

I would check vacuum hose, coils and plugs and upper intake rubber hose elbow coming from the pcv valve, I there a check engine light?

 

So I finally got around to doing a bit of diag on this thing. I have steady pressure at idle at around 34-35. When the truck starts acting up, fuel pressure increases 1-2 psi from 35, and engine load increases. I did not get a chance to remove the vaccum line to the regulator simply because I was afraid it was going to end up cracked and broken. I'm going to monitor the IAT vs. ECT tomorrow with my Scan-Gauge. Unfortunately, there is no CEL. I've found the emissions monitoring to be **** poor on this truck.

 

The pressure increasing while it's running rough probably just means the vacuum gets low because of running rough.

You can simulate pulling the vacuum line from the fuel pressure regulator by just leaving the engine off but cycling the key back and forth a few times between "on" and "off" and checking the fuel pressure. It should be up near 40 when you do this.

 

Have you cleaned the MAF?
Has the IAC ever been replaced?

 

The MAF was replaced with a Motorcraft part. I accidentally cycled the key like Krewat described and it was around 40. I'm ruling out the fuel regulator. The IAC valve isn't a bad idea, but the truck had the issue under throttle too.