(Warning I did not spell check.)
There is only a limited number of Vacuum Lines going through the Fire Wall.
The Black one is a vent and simply goes iniside and connects to nothing.
There is a Brown with Blue Stripe and Brown line that are poart of your Vacuum shut off setup.

All of the other Vacuum Lines can be disconnected and the supply sides plugged off.

If you sound is still there after that then it is not likely it is a sound from the Vacuum. I gues to be sure you could move on to disconnecting the Brown with Blue Stripe and Brown just to make sure the sound is not coming from the Shutoff Valve on the Steering Colum Lock.

You can disconnect the Vacuum Line at the EGR and plug the vacuum supply side off. That should keep the EGR from openig.
The test for the EGR itself should be similar to a Car EGR Test of the same year. You disconnect the Vacuum Hose at the EGR and hook up a Mighty Vac or other vacuum sourse to the EGR. As you pump on the Mighty Vac and the vacuum rises the EGR should open and your engine should start runing rough when the EGR opens.

You might try disconnecting the ALDA Line and plugging of the Boost side and go for aride and see if it still smokes black.

You never said if your exhaust smells like burned Oil or simply normal.

If the Turbo Charger is leaking Oil especially on the Exhaust side it will blow black smoke. If you disconnect the Exhaust end near the Turbocharger and look inside if you see a lot of shiny wet looking carbon Oil is coming from some where and getting into the Turbo Exhaust end.

That does not entirely rule out the Oil coming from the Engine. You can see that by removing the Exhaust Manifold and looking into the Exhaust ports of the head. If Oil is coming out of their you will see that shiny carbon.

You can also pull an Injector and look down inside the prechamber. If the carbon in the prechamber is shiny and wet looking you are burning Oil. When the Injector is out you ca look at the base of the Injector Nozzle were the pinte/needle sticks out and see if the metal around it is all burned or erroded away.

The Compressor side of the Turbo Charger can also leak Oil and throw that Oil up into the Intake. If that is the case right after you start smoking black you would expect that if you took a peak in the Intake Maifold there would be Oil. Especially in the area closest to the Turbo. And, you would also expect to see the results of Oil in the precombustion Chambers if the Cylinders closest to the Turbo. That shiny carbon I have spoken of.

You did not say if your crankcase Oil level is falling.

Your Injectors would have to be incredably bad to blow black smoke. I think if it was the Injectors your idle would be worse. Mine had 198K on what looked like the original Injectors the Nozzles of which were in bad shape.

You did not say you were using only Diesel Fuel or if the previous owner had used only diesel fuel.

Of course your Air Filter and Air Inlet need to have no restriction.

I suppose if enough Oil is gettin up into the Air Filter Housing (not the CA Air Filter Housing) from the Blow-by that could also cause balck smoke but you can discnnect that breather tube and go for a drive and see if you still have black smoke. If with the tube disconnected you no black smoke you know it is the Blow-by causing the issue.

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84 300D, 82 Volvo 244Gl Diesel