I own a 92 300E (M103 sohc engine) with 122,000 miles. Cold start is no problem. Smooth, cold startup. However, after engine is warmed up, there is a problem. If I shut off the warm engine and come back within a short period of time (say five minutes) the engine starts normally. If I return to the car after more than about ten minutes and attempt to start the car, the engine will run slightly rough for about 10 seconds and then smooth out. The degree of roughness will vary with longer times between starts. In all cases, after a few seconds of rough idle, the engine returns to a smooth idle. Any suggestions? Just changed plugs, distributor cap, and rotor as part of normal maintenance. Suspect some type of fuel problem.