I recently had the same fast idle on startup issue on my 1995 E320. The cruise control also did not work. It turned out to be the T/LLR module, which is the electronic control module on the inside of the car under the passenger side front footwell. My unit was also clicking rapidly, which helped me to locate this part as the cause. Good used ones are available on eBay (the part number for mine was 1245455532). I bought one there and replaced it and everything runs fine now, including cruise control.