84 500 SEC hard starting and has trouble running when foot comes off gas pedal, rpm goes under 5 and car shuts down. Problem just started, I thought I had run out of gas at first because car would start but shut off when foot was off gas pedal. So I put in a container of gas and she started right up. I drove home and problem reappeared on next start up. I hear a humming from engine around air filter, I placed my hand on what I believe to be cold start value and feel a hard vibration. I do not know if its the value or fuel pump causing the problem. Can somebody help me? Car will not idle at correct rpm.
One thing different I noticed is when opening gas cap I no longer hear vacuum sound that I usually hear after driving car. Last Test I ran turning ignition key but not starting car, I did not hear fuel pump start. Can anyone give me some pointers on how to narrow down source of problem? I found #11 fuse blown, looks like spark plug wires may have touched idle control unit and shorted it out, that is what i believe is the problem.

just wondering what ended up happening with your car.

I am having similar problems on my 420sel.

I found that a circuit burned out in the electronic control unit on the firewall, took off the cover and saw the damage. I ordered a new one over the internet and replaced it in 2 mins. Car has run fine every since.