If I had seen this thread before now, I would have suggested all the things you did, exactly, since that is what I did with my 300TE two and a half years ago -- same symptoms except also occasional stalling when coming to a stop.
That idle control valve hose to the manifold is a pure pain, eh? Took two of us to put it on (with the clamp, too!). Mine were rock hard and loose on the barbs, so a leak was a certainty.
I have the new engine mounts, will be installing them as soon as I get my brother's restoration project out of the garage (windshields go back in on Tuesday night!)
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!