Look into the archives for the alda circuit. The system that controls it seems to soot up over time on most these turbo cars. Almost a long term maintenance item.

There is a port on the intake manifold that reads the inside boost pressure. A feeder hose to an overboost device and then the hose goes on to control the alda on the injection pump. If this system obstructs and they will . You get boost pressure from the turbo. Yet the alda does not get the signal to increase fuel with the boost. So power is very low.

Always a mandatory check like the linkage was anytime an issue like yours rears it's head. Tons of information in the archives as it is such a common issue.