Leon - Interesting history, I think every car has a story. About dealers, I think most have some knowledgable mechanics, it's just that they are not necessarily the ones that work on your car. Before this car my wife had a '77 240D that a I got form a guy at work who had it religiously maintained by the dealer from new. When I got it the hood hinges had never been lubed and had seized and enlarged the holes. PS. my brother was a mechanic but not for Mercedes.
Now back to our problem. I have checked a bunch of things and they are all OK. The only thing out of spec (besides the idle timing) is that the dwell is low.
Things I've checked.
1. Idle position sensor.
2. All inputs to the EZL (except crank sensor).
3. Idle control valve, had it out and cleaned and tested it on the bench (5 ohm, opens and closes smoothly). At idle it draws a little under an amp (which should hold it closed).
4. Idle injector (removed connector with no change, so it is getting the gas from somewhere else).
5. OVP (didn't check Zener cutoff but power gets to all the right places).
I also had my wife put it in gear and step on the brake and the advance lessened both with and without vacuum. This leads me to think that if the engine slowed to the spec the timing might be right as the only EZL inputs are RPM and vacuum.
I am about to break down and get a scope and start scoping (a lot cheaper than an EZL).
Does anyone have the pinouts of the diagnostic connector? The print is too small on the schematic and I can't find them anywhere else.