After checking what Steve recommends check your fuel supply particularly the fuel screen built into the fuel tank and the fuel filter. Of course your fuel tank would need to be emptied before removing the in tank screen. My vintage 126 380SE sat unused for a few years and developed an intermittent (after 10-15 minutes of operation) misfire and stalling problem when I put it back into service. Turned out the gas tank had corroded internally and would periodically clog the built-in gas tank screen. The intermittent nature was caused by the peculiar design of the fuel feed in the tank. Since the bottom of the tank is flat and couldn't locate the fuel pickup at any one low point in the tank, they installed a 6-8" tall plastic cup in the center of the floor of the tank and installed the fuel pickup in the cup. Of course the fuel would have to enter the cup from somewhere once the fuel level got below the top of the cup so MB (not content with placing a 1/2" hole in the bottom of the cup since the fuel could drain out on long, 130mph corners on the Autobahn or race track) installed a venturi device that would use the fuel returned from the fuel distributor to "suck" fuel into the cup. Only problem is that if the tank contained sediment (rust in my case), the sediment would be sucked into the cup, stirred up by the return fuel flow and would ultimately lead to plugging of the screen after X minutes of operation. Once the car sat for a few minutes, it would restart and run fine until the cycle would again repeat itself. You can get an indication of whether your tank is rusted by looking in the fuel filler neck and by removing the fuel level sending unit and peering inside. It goes without saying NOT to create sparks or use open flames and technically vaporproof flashlights or lights should be used to view the internal condition of the tank. Good luck.