Do you have a vehicle speed sensor? When you take your foot off the gas, the switch on
the throttle position sensor closes and unless the computer knows the van is moving, it
tries to achieve an idle speed using the IAC. When the engine continues to rev (as you go
downhill) the computer thinks the IAC is stuck open and sets a code. This is not anything
to worry about. If it bothers you, just keep a tiny bit of pressure on the pedal when you're
coasting and the CEL should stay off.