SO. I love this little truck.
But that being said. I'm about to drive it off a cliff.

Rough idle.

New parts.
MAF, IAC, TPS, plugs, wires, coil pack, both o2 sensors, fuel filter, FPR, no vac leaks.
Cat is out. with a big hole in the bottom. (Will replace shortly)
Fuel pressure is at 35 psi, key on engine off.
28 engine running.

Problem is.
With MAF plugged in idles smooth. But down the road, seems like its starved for fuel, bogs down and wont hardly hit 15 mph. NO CEL when plugged in
With MAF unplugged, idles a little rough, but will run down the road just fine. But CEL comes on.
This is the 3rd MAF in this truck and they've all done the same thing.


This is a no EGR 4.0
What am I missing?

 

Could be the computer is the problem

When MAF is unplugged computer will stay in Open Loop so doesn't use any sensors just runs from the air:fuel mix tables in memory for a 4.0l engine

You can confirm this by plugging in MAF sensor and driving while engine is Cold, its also in Open Loop until it warms up a bit, maybe 3 minutes

If engine still runs poorly cold with MAF connected then MAF circuit in the computer is most likely the problem

Open top of computer and check the 3 blue capacitors, common issue after 20+ years

Should look like this: Ford EEC-IV

You can see the 3 blue caps, if one has leaked then odd things can happen, there is no one problem for that
under $5 to change them if you have soldering skills.

MAF test info here, worthwhile before ripping into computer: https://therangerstation.com/tech_li...CleanMAF.shtml
About half way down the page is test info

I use sewing needles to pierce wires to test while they are connected