I have 15,000 miles on a 2002 TL-s, and lately the throttle will seem to stick in the closed (idle) position. This leads to some rather jerky starts. Upon examining the throttle plate, I found a dark brown, crusty build-up of some relatively hard substance on the plate circumference (edge), almost exclusively on the upstream side (when open) and extending about 4 mm in from the edge. There is also some minor corrosion (white / powder, like Al oxide) on the throttle body adjacent to where the throttle plate seats at closed position. This causes it to stick closed (mostly after sitting overnight).

Has anyone else had a throttle sticking at the idle position, or noticed odd corrosion and / or contamination on the throttle plate and / or throttle body interior? Any thoughts?