There are several things that can make the D-Jetronic idle fast -- loss of vac retard, which increases the idle timing by 12 degrees, stuck aux air regulator (aka fast idle valve), which can be cured sometimes by a sharp tap to the top of it, vacuum leaks in the tranny modulator, door lock system, vac retard line, or the seals between the manifold halves (eight round rubber rings).

I'd make sure everything else was OK before just adjusting the idle speed, it should never change much except for fast idle on start. I don't get fast idle unless the car is still slightly warm from a previous run, but I don't care since it runs fine otherwise.

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!