I have a 2001 Expedition XLT 4x4 with a 4.6L engine. The idle flutuates between 550 and 800 RPM up and down when I am stopped with my foot on the break. This only happs once in a while and it seems like the engine needs to be warmed up. I was told this could be a vacuum dump valve for the speed control. Any ideas?

 

It's more likely an issue with the IAC.

 

It quites when I put it in park. Would that happen with a IAC problem?

 

I dunno - but it's not that difficult to remove the IAC and throttle body and give them both a good cleaning.