Did you get the overboost issue fixed?
Check my posts about it.
I have been fighting an overboost for quite a while now.
Meanwhile driving 100km to a new workplace and back every day, having a new baby, moving to another country with a 2ton trailer and buying and fixing up a new house.
things became better, worse. Changed during, other things broke..
They are old cars.
But in the end its not a very big deal.
And the only thing that can happen, is that you have a slow car.
First! check that maf. Swaptest it with one that works from a junk car or friend or random person at the gasstation.
If thats ok. then go to the vacuum system.
Google a vacuum diagram for your engine. Print it and keep it at the car!
Then go buy 5 meter of 3mm, and 5 meter of 5mm tube. Silicone or rubber benzine hose. Something strong and durable. Dont know those sizes feet or thumbs.
Cut to size and replace every vacuum line one by one. Its a very easy job, and very rewarding.
Now blow on those lines one by one to see if there is an obvious culprit.
If it lets your air through, its leaking. also check the couplings! Check the hose from the vacuum pump to brake booster.
For instance where the brakebooster goes through the rubber at firewall, my rubber leaked. Later my heater valve leaked. new ones were cheap and relatively easy to find.
for the big hoses on the ic and pipes. Get some decent hoseclamps. Mine never came off.
They are cheap, very easy to reach and swap..
Now the last thing is probably the vanes being stuck by coal residue.
Push the rod going into the turbo. If it doesnt go smooth and easy. They are stuck and will throw a limp mode.
I am going to see if the mr muscle trick will solve it.
I spent a day reading and looking through results of people trying it. And for a lot of people it solved their sticky turbo vanes problem without any issues.