I found this thread trolling for something else:
Speaking for a 1985 380SE-
Most of the above is all true.
ALWAYS begin any trouble shooting on a car that IS PROPERLY TUNED-UP by first checking vacuum lines and boots for wear, brittleness and leaks. There are two lines that are under the plenum (standing at the front of the car facing the engine- behind the idle control valve) that go to a thermo switch at the passenger head bank. They can be a bear to get to without removing the plenum/ intake.
Once I had a bad hesitation. It was the t-junction vacuum that also connects to the switch that is on the outside of the coolant reservoir.
Second- you must perform a fuel pressure test. There are plenty of strings that go over that. THE SLIGHTEST leak in the system will cause problem. For example, I once had a crush washer between the fuel pump and the aperture that was very slightly diminished by sodium chloride. The damage caused pitting and an air hole that cause hesitation on acceleration.
Welcome all to owning a old Mercedes. ALL THINGS OLD NEED MEDICARE- in this case, Mercedes-care.