ok, I am going to mention a few things that have caused my bog down problems in the past with my 1986 740Turbo Wagon.

Check:

Turbo intake hose-make sure there are no cracks where the nipple comes out and attaches to the PCV hose

Check the small hose on the drivers side of the intercooler-check the underside of hose, this is where it usualy splits.

Change your fuel filter, maybe add some drygas to an empty tank an fill her up with the good stuff...

Take off your PCV hose (the one that connects to your turbo intake hose across engine to the PCV valve. Make sure it is not full of any crud, do the blow test, if it is clogged clean it out with a metal coat hanger (or something of that nature) and use some carb cleaner to get the rest out.

And of course, fix your exhaust.... that is a good recommendation!

If still in woe of what could be the problem after that you will have to start by replacing that which should be replaced, check timing, intake leaks ,etc

Best of luck to you!

Best Regards,

Anastasia
1986 740Turbo Wagon 380,000 miles...