This topic has come up several time recently at kia-forums.com.
While attempting to accelerate, the engine may drop back down to idle speed for up to twenty seconds. This has been reported on both diesel and gasoline models and both on automatic and manual models. The problem, so far, corrects itself. But, while it's happening, dangerous situations can occur.
More here:
-- Christian '02 Sedona EX (3.5)