2006 Mercury Montego, 17,000 mi. I have a problem with the engine rpm surging when slowing to a stop in traffic, or dropping and then surging when stopped. The problem is intermittent, and happens with the ac on or off, cold car or warm car. The idle is smooth at 650 rpm the rest of the time. The dealer thought they knew what was wrong and replaced a wiring harness to the throttle body. The problem was still there. They now have the car overnight to try to create the problem (remember it is intermittent). The car is about to go out of warranty, and i want to make sure it gets fixed. Check engine light is not on. I think it in the computer, anybody else had this problem?