I did this to mine today... Pretty damn near perfect now... might need to take it off and clean it again. This is from
http://www.explorer4x4.com/tips.htm:
Fix for a Missing Engine
Posted by: Jack Lobdell
Many Explorer owners have experienced "bogging" or "missing" or just unsteady performance in their 4.0 engine and have been frustrated by lots of expensive "non-fixes". After riding on a plane next to a manufacturing trainer from a company that builds OEM replacement auto electrical components for places like AutoZone and CarQuest, I tried his tip. He says that Ford have these problems more than other makes and the 4.0 engine seems to be more susceptible to the problem than other Ford engines.
It seems that a "missing" engine culprit is actually the computer's sensor inside the Mass Air Flow Sensor (MAF). It eventually just gets a little dirty or builds up its own patina in the filament wires. A dirty or slightly patinated filament will send the wrong air reading to the computer, saying it is getting more air than it really is and the computer will tell the EFI to send in the wrong mix of fuel, thus, the bogging. The patina seems to form faster if you live in a damp climate. I don't so here in New Mexico mine went 82K before it developed a small "flat idle spot"…it would run just fine but the idle began to drop every few revs from 700 to 500. No big deal.
If you have had bogging or missing or idle spots, about every 25K miles plan on this quick cleaning job:
When your engine is cool, remove the wiring clip from the side of the black plastic sensor part of the MAF aluminum body. To remove the MAF interior sensor wire, you will need a Security Star (Size T15 or T20) screwdriver or screwdriver bit for a power screwdriver. Remove the two security star-head screws and carefully remove the sensor. You will see the two sensor filaments…they look almost like the filaments on a light bulb. Carefully spray the filaments with an O2 safe carburetor cleaner, such as Gumout. Let it dry thoroughly. I help mine along with a careful blast or two of canned dry air. While it is drying carefully wipe the aluminum mount surface of the MAF body if there is any dust there, but be careful not to get dust in the mount hole. When the sensor is dry, replace the sensor back in the MAF body and secure with the security star-head screws. These don't need to be torqued down, just simply hand tight. Replace the wiring clip. Then start up your engine. You should have solved any bogging or missing problems. My flat idle spot is ancient history.
