First, thank you all for your replies. And excuse the length of this post.
I have had the car for only 2 months, however I am pretty sure that the wiring harnes has been replaced. This is because if you look at the DIY on mercedes shop there are pictures detailing the process and you can see that the new harnes although almost identical to the old one, it is slightly different, exacially on the connections to the thermostat. Mine looks like the new one, and it is not flaky.
Part of my problem is fixed. I looked for any disconnected vaccum lines and I found one big diameter line disconnected at the intake manifold, btw the intake and the cylinder head. I plugged the line back in and started the car. Now the idle does not nearly flunctuate as bad. Before it would go up or down by 400-500 rpm, now it is more like 10-150 rpm. I think I can still hear a hissing sound (maybe vaccum leak, but it is hard to accurately tell b/c of engine noise. Do I have another vaccum leak? I strongly belive that whatever is is due to the recent work I did on it. I worked around a few vaccum lines.
When testing the EGR, it does hold vaccum, and I can hear the membrane inside click (open or close noise), however, when the car is idling andf I apply vaccum it does not make that much difference. But, I KNOW the egr sover pipe is very clean.
Do you guys think I have another vaccum leak, or my egr is bad? The engine had no idling problems before when the egr crossover pipe was completely clogged. (It was totally clogged in the last 5-6 inches of the pipe. I think that now that pipe is clean, either there is an egr problem, or I must have damaged a second vaccum line.
When I broke a couple of vaccum lines in the very front of the engine, under the cover, I replaced 2 sections with a generic rubber vaccumn line from the autoparts store. The diameter of this line was slightly larger. Could this be a problem?
Thank you again.
Tony