Thanks for the tips. I looked at the above posts and there is a lot of useful information there.
I poked around for a while (temp sensor, etc.) and couldn't pinpoint/diagnose the problem as I don't have all the tools. In the end I took it to a mechanic to diagnose the problem. He measured the fuel pressure and checked the fuel distributor, fuel pump, etc. It turned out to be a defective EHA (Electro Hydorlic Acutator). He replaced it, and the engine runs real smoothly now - cranks up without even touching the gas pedal. Problem solved.
190E 2.3, 1988