I'd pull the manifold. Replace injector seals on all the injectors, check out the AAV (probably stuck), replace the idle air hoses and the seals between the manifold halves. Replace the rubber parts of all the vac lines, and replace the hose to the MAP -- these are all probably leaking to some extent.

Clean the idle valve, and when you put it all back together, set the idle to keep the fast idle with the AAV all the way open less than 1500 rpm. With no vac leaks, this should be possible. May lower the idle hot in gear to about 500, but if you don't have stalling problems, this will work fine.

That surge is a real PITA, eh?

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!