My friend drives a 2006 Ford Explorer 4X4 (I believe the Eddie Bauer model) that on startup, when in park revs to about 6,000 RPM eventually stalling out. When restarted, the car doesn't stall, but does surge and idle VERY poorly. The transmission also shifts horribly, occasionally slipping, and the engine hesitates when accelerating. This all makes me think that the throttle position sensor went bad, however the check engine light came on the last time I drove it and the last time she drove it the powertrain/4X4 malfunction light (indicated by a wrench light on the gauge cluster)
so many things can do that, but those are known for bad throttle assemblies
the car also has 123,119 miles on the odometer.
not sure if that's important but just thought i'd include it