I have a 1980 300SD turbo 365,000KM and have recently acquired a 1983 300SD turbo. I made a big mistake and didn't drive the car before I bought it, as a friend had checked it out for me.
The car is in near mint condition with 200,000KM. It has a serious problem with engine performance especially at low speeds. It is totally gutless, ie no acceleration off the line until the turbo cuts in. If you are travelling in town at say 40km/hr and push on the throttle nothing happens unless you push it through the floor.
The 1980 has way better acceleration between lower gear changes and responds quickly when you push down on the throttle at any speed. The 83 will go great at high speeds on the freeway but is a dog in city traffic. You have to push the accelerator to the floor to get moving. It seems to have no acceleration until the turbo cuts in

I have been to and talked to 3 local shops and spent money to get only advice and no resolve. Some say I need a transmission rebuild others say, IP problems others say valve ajustments and timing chain. Others say fuel problems. I can see myself getting empty pockets fast to fix both IP and tranny .
I changed all filters with no improvement. It seems to go fine once the turbo cuts in but it accelerates painfully slowly before the turbo cuts and seems the worst trying to speed up from around 40K/Hr.
Lack of fuel doesn't make sense, as I can fly on the freeway and maintain high speed on hills on cruise control. I do believe that the transmission could need rebuilding but I don't know if that can be a key to the power problem. Another possible clue is that, it will hardly move at all if you try to drive out of the yard without warming the car up for a few minutes.
Other things which may be of importance is, that it starts instantly and runs smoothly in freezing conditions. There are no fuel leaks anywhere, and the engine compartment is spotless
I would much appreciate any suggestions on where to go with this.