Hi. I'm new here. Have been given a 1991 W126 300SE by a friend and am slowly breathing life into a car that has stood for many years. Some suspension and brake work and she now drives but is very difficult to start, often requiring 10 minutes or more of the ignition being on before an attempt can be made. Once started she runs fine for 3-4 days and will then suddenly stall. Start up afterwards is immediate but she won't idle without pressure on the accelerator pedal. I have replaced the fuel pump and filter, the over volt protection relay and the idle control valve and re-soldered the circuit board in the fuel pump relay. Yesterday it did it as I got home so I removed the air filter and started her again. What I observed was the ICV clicking and it time to this the plenum in the throddle body was moving up and down, almost like a heart valve beating!. Revving the engine to keep her going would produce a hesitation, also in time with the beating heart! So I disconnected the electrical feed to the ICV and the beating heart stopped, the engine revved freely (no hesitation) and idled, albeit at around 400rpm and roughly! It is obviously electrical and I am guessing to do with the signal to the ICV but has anybody experienced anything similar or know where to look? If I leave the car overnight all will be well in the morning for a few more days and then it will happen again