I have a 96 C280 with 82,000 miles on it. Several times when I start the car nothing happens. The battery is fine as will as the starter. This is intermittent and goes away after I try several times. Other times the car starts up VERY VERY rough. It feels as if the whole car is Shaking violently. After a couple minutes it goes away and is fine. This problem is also intermittent. I took the car into the dealer twice. The first time they said that since it was intermittent it was very difficult to determine what was causing the problem. The second time, they couldn't find anything. Any suggestions?