Idle should be 650 warm out of gear and 500 in gear, cold will be as high a 1500 on start, dropping as it warms up (quickly!).

I would also check the vacuum line to the modulator, unless replaced the rubber is completely dead by now. I replaced all the small connectors on the TE when I got it four years ago and cured a number of similar ills.

You should also check the engine and transmission mounts -- all are likely dead by now, and will cause both rough idle and thumps when engaging the tranny. The engine is sitting on two springs with no damping when the glycol leaks out of the engine mounts!

You can check them by just looking -- if you cannot see the trapezoidal steel insert on the bottom, or the "rim" in the center of the mount is less than 1" away from the frame, the mounts are shot, replace them. Makes a huge difference. If the tranny mount is soft, replace it too.

Peter

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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!