hot spark plug wires
I had exactly the same problem yesterday nite, Tuesday, with my 87 300e. (I had filled up the gas tank Sunday nite with Mobil super.) I checked the spark plug wire connections & noticed the wires were really hot, too hot to touch. I had just completed a 30 minute highway drive averaging 70mph. I also found when I lifted my foot off the accelerator for a second the car ran smoother, as evidenced by the economy gauge needle moving to the far left, the best reading. This suggests to me a fuel flow issue, maybe fuel pump relay, which is discussed as a cause in thread 36327, entitled "300e won't start. Fuel Pump? How to check?", which you should read.
BTW, should the spark plug wires get that hot? Does it suggest resistor end problems?