Sounds like the ECU (engine control unit) may running in a simple "limp mode". It will do this when one major sensor is out of tolerance, or fuel pressure is not correct. This allows you to drive the vehicle, albeit at a simple, slow pace. Or, you can have an ignition break down. A coil can break down under load, but idle just fine.
Unplugging the mass airflow sensor to get it to run better leads me to think its still fuel related. With the MAF unplugged, the ECU is not using it to detect the amount of air the engine is seeing or using, thus adjusting the fuel pressure to the fuel rails which feed the fuel injectors.
You need to check the fuel pressure at the fuel injector/fuel rails. There should be a valve on the rail that allows a fuel pressure testing guage to be connected to. This test lets you know that yes, you have good fuel pressure, or no, you don't. If you don't, then the fuel filter or the electric fuel pump (in the gas tank) are suspect. I don't believe these engines use a fuel pressure regulator which is used to route fuel back to the tank from the fuel rails. Instead, the pump is cycled on/off, based on sensor input to the ECU. Ford switched to this type of system in many of their vehicles in the late 1990's to early 2000 years, to help prevent vapor lock in the fuel lines.
If its the fuel pump, some find it easier to remove the 6 bolts, the fuel filler tube, and the wiring harness to the bed and remove it to get at the gas tank top, where the plate and its circular hold down are easily accessable.
Last edited by bucko; 09-16-2014 at 04:55 AM.