Wipers Slowing Down
 

For some time now my windshield wipers will slow down when left at the same speed for more than a few minutes. Its not that the intermittent speed slows down, its the wiper actually moving (or hardly moving) across the window. I know its not how the wipers slow down when stopped. They slow down while driving. If I move the stalk to a fast speed and then back, they start going at a normal speed.

Do have a bad motor or is this some feature that I never noticed?