For the 1982 model, the turbo starts working around 1300 to 1500 rpm. I assume that you have tested the ALDA boot circuit to be sure that the switch does not cut out the fuel too early. The turbo has a wastegate valve to prevent overboot also. If it starts open too early bleeding the manifold pressure, the turbo will slow down.

Why this happen after you change the fuel filter? Did you work on any other areas at the same time that could restrict the flow of air or fuel? There is a fuel pump attached to the fuel injection pump. I do not know how to test this fuel pump if it is dying.

Howdy,
I cleaned out the boost sensor line and for the purposes of this problem, have bypassed the cut-off valve thus running sensor line stright to the ALDA from the intake manifold. I tested it under load and was in fact getting positive (boost) pressure from the manifold. I don't know how to further test the ALDA without getting into some fairly complicated plumbing. I'm hoping the shop guru can discern thr problem with the same ease possessed of a Palm Beach ballot official counting a ballot.

I didn't get into any other areas whilst doing the filter change. I am a firm believer in limiting the number of variables in an equation. Following the filter change, I went on the cursory test drive and noticed the symptoms. I've been doing my own maintenance for years and while this is my first MB, I I do feel comfortable under the hood. On the plus side, since this problem occurred five days ago, I have become much better acquainted with the inner workings of the 300D. Having driven SAABs and Volvos for years, the MB is a real treat to service. The build quality and materials are remarkable. I'm really enjoying it.
Thanks agin!
J.