I have the exact same issue. 2004 f150 fx4 w/ K&N filter. After the engine warms up and i put it in park, the idle will flucuate and at times the engine will stall. It seems like the throttle body cleaning is the fix? My question is, what is this throttle body and how hard is it to clean? i'm capable of a little more than basic repairs. Could I do it or should I engage my mechanic?

Additionally, the 2004 ford manual stresses not to clean the TB bore & plate because they have a special coating?

thank you all for your time,
rob