Expedition Running Rich?

I recently noticed black soot stuck to the bodyside (around the tailpipe)and rear bumper of our 1999 Expedition LTD 4X4. It has about 70K miles on it. The acceleration is poor. I checked the oil, it is down a bit, but due for a change, so probably normal. A friend of mine who knows a bit about this vehicle said that a friend of his had a similar problem with an Expedition, that it turned out to be some valve on the intake manifold (kind of like an EGR). Anybody have any ideas? Thanks.

have your mechanic check the idle air control valve, it's on the back of the intake manifold, on the passenger side.
hth
Rick, Ore