i loaned one of my trucks out recently and it came back to me with a problem i just can't seem to fix.

he said he was driving it and one day, it just started to act like it was starving for fuel (very low surge dropping from idle to ~200RPM). the truck also falls on its face when i give it gas (starting in 3rd gear) but will accelerate if i touch it very very lightly.

the kicker here is that i can let the truck warm up, and it seems once the thermostat opens, idle comes back fine. however, it will only last for a few minutes before it kicks back to the surge issue, bouncing between these two states constantly.

i read through forums and came to the conclusion that it must be the tps, as it is on many other trucks. i have replaced with another motorcraft tps, and the problem still exists. i also replaced cap and rotor (although not plugs or wires) and fuel filter/fuel pump relay/engine control relay. the problem exists on both tanks, by the way.

i have cleaned the maf, maf connector, tps connector, and thermostat connector.

i'm running out of things i can think of off the top of my head, of course plugs and wires but i replaced those right at a year ago. i have also only put 13k miles (no load, driving to other states for work, so all light highway miles) on the truck. (truck has 133k miles)

any advice would be appreciated. thanks!

 

I had the same problem. I ended up finding two issues, the upper intake gasket was bad, and the bypass valve on the top of the throttle body was bad. I would check these two things. I hope this helps.

 

check your fuel pressure at the rail fitting. Mine started doing that and it got worse and worse until it stopped running. both fuel pumps went out.

 

haven't had a chance to do either of these yet but any other input on things i should check while i'm trying these ideas?

 

I just replaced both fuel pumps and in the rear tank, the engine would not run. I have the bed off so access to the tanks is a piece of cake. (Carrot Cake that is) the pump was from a wrecking yard. After installing it , I could hear it running but the engine still would not run. I turned on the rear pump and checked the fuel rain for fuel pressure. Nothing. I pulled the pump, and noticed there was no fuel in the pump itself. I checked the small inlet at the bottom of the pump. There is a small rubber check valve that was stuck closed. Took a small screw driver and freed up the rubber check valve. re-installed the pump and the engine runs perfect. I put a can of Seafoam in each tank. Seafoam IS a miracle in a can. I am skeptical of these kind of products but seafoam has proved itself to me.