I have a 2000 f150 4.2 liter motor 2WD. The truck idles fine. At a light if I accelerate gradually it's ok. But if I step on it too hard it almost stalls. A little background, I started it one morning and it backfired. It gave the code for a bad fuel position sensor. I had the dealer replace it. When I went to pick up the truck he told me of the problem. When I asked what it needed he said he would have to diagnose it to determine what was wrong. I just spent $500! The last diagnosis cost me $700. By the way I got the feeling he knew exactly what was wrong but wouldn't say so. (He told me I needed a lower ball joint. When I got the truck back it needed a stabilizer link.) So far I've replaced the plugs, wires, coil pack (6 cyl unit), and crank sensor. I have also cleaned the MAF sensor. Still have the same problem and can't find a vacuum leak. Any help would be greatly appreciated. Also it isn't showing any codes.

 

have you tried the fuel filter yet?

 

Unplug the MAF and see if it runs better. If it does try cleaning the MAF again. It may need a new MAF. If it doesn't run better, you'll have to look further.

 

Yeah I've replaced the fuel filter, and cleaned the MAF sensor twice.
I'll try unplugging it and see what happens.