Runs like a champ but really rough idle sitting still

I drive a 2001 Explorer Sport Trac with a 4.0 SOHC V6. This problem has been present for several months. While listening to it it sounds similar to a backfire but on the air intake side where the air goes into the throttle body. When this happens the trucks shakes a bit side to side or forwards and back. Sometimes I feel like it might die. When I drive, it runs great, good acceleration and no problems with full throttle. I have a buddy here that seems to think that one or more of my intake valves are bad or burnt and needs to have the heads machined. Just looking for some help from real experienced people. THanks for the help!