Hi, Mike
I question why the Alda would suddenly need adjustment after the car ran so well before. Boost can be lost if the flapper in the turbo waste gate gets hung up and fails to close.
This happened to my '87 and the solution was to free it up using some WD40 and elbow grease (WD40 to wash away the carbon stuff that was causing it to jam, there may be stronger stuff available but it wasn't necessary). My mechanic friend was planning to send the turbo to be rebuilt before this little salvation
I looked at a '87 300TD once, before I knew anything about the 603's and passed on it because it was a real slug. Knowing what I do now, I believe it had a plugged up trap oxidizer and possibly the wastegate was leaking. It was being offered for a quick sale and looked fine but the way it ran it felt like a 240D
OTOH, I have two wagons already and my wife would probably leave me if I bought another
I hope your able to restore the performance without messing with the ALDA and losing some fuel economy which is so geat in the 603 engine.
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230