I have a 94 E500, 65K miles. This evening I drove the car from work to the airport (about 50 minutes) to pick up my wife and it was running fine (ambient temp in MN Ė 78 degrees). However, on the way home the car exhibited a noticeable miss. It felt like a surge every 5-10 seconds. I was worried it was going to stop running, but it did not. I could accelerate fine and it didnít seem to miss when I accelerated hard. However, driving along at a steady speed you could feel it hesitate in the 5-second cycles. When I stopped at a light with the engine at idle I could see the tach drop slightly matching a rough idle at the same time. My car has the stock chip and has never exhibited this problem previously. Any idea on things I should check? Thanks for your help! I do the work on my cars myself and take pride in understanding the mech. And electronics of these fine machines. The problem is knowing were to start looking and hopefully someone else has had this problem and can help me out.