Brook, first of all let me welcome you to the site. I'm sure you'll find that this is one of the best Ford Explorer resources on the web.
Let me explain why you need your MAS. Simply, you're truck will not run without it. The MAS is a critical sensor that the engine computer uses to compute fuel flow and other parameters that are vital to proper engine operation. I suggest that you upgrade your KN drop-in to a KKM or KN performance kit. These kits consist of a large conical filter, brackets to support the new filter and MAS (bye bye airbox) and an adapter to fit the large filter onto the MAS. If you are still worried about intake restriction, upgrade your throttle body to a BBK 66mm unit. You may want to upgrade your MAS also (I recommend the Vanir units), but you probably will not notice any difference with an upgraded MAS until you start getting really aggressive with the mods. I have a supercharger on my 4.0 and still run the stock MAS. You might also want to think about a performance chip, such as a Hypertech or Superchip (JET chips suck).
Hope this helps! Good luck, and welcome again to ExplorerForum.com!
