My car has done this off and on since day 1. It will act up for 2 or 3 days and then it will go away. Probably happens about 2 or 3 times a year. It will not happen in the winter, usually when it is warm and humid outside.
It pi$$es me off, but I guess it is a feature. When it happens I can "idle" at 50 MPH in 5th gear!!!!!
