There may be a leak in the fuel injection system. If there was gas inside the plastic intake, and it found a spark, that would have caused an explosion inside the plastic intake. Where it found a spark to set off the explosion, I am unsure, but there should be no fuel inside the plastic intake, only air. With the EGR valve in there also, it is common to have some sludge type of build up, but gas would only be there if you have a leak in the fuel system inside the plastic manifold. I checked my fuel injection system by jumping the fuel pump relay, and looking inside the plastic intake with a mirror and a flashlight, after removing the throttle body. You could also remove the top of the manifold, and reconnect the fuel lines. Here is the video I used to jump the relay. This will turn on the fuel pump, and keep it running while you look at the fuel system for leaks, without starting the truck. The part about jumping the relay is about 18 min. into the video.
