To trouble shoot for other Vacuum leaks you disconnect and plug off one system at a time. If then one you disconnected and plugged off improves the Vacuum then that system is where the leake is.

As an example you have only so many Vacuum Tubes going through the Fire Wall. The one with the Check Valves is the locking System. To see if there is a leak in the Locking System; under the Hood disconnect the Vacuum Line goint into the Check Valves and plug that (you are disconnecting and plugging the line closest to the Vacuum Pump). If your shutoff starts working OK then that would be an indication that the Locking System has a leak.
The Solid Black Vacuum Tubing is a vent line and is connected to nothing inside.

If you have checked all the Vacuum Tubes going through the Fire wall what is left is the Tubing that goes to the little valves on the Valve Cover, the Transmission line and the Trans moduel and the EGR line if you have one.

On the Transmission Moduel the Cap the covers the Adjustment has been know to Crack or even fall off.

Inspect all of the Rubber connectors under the Hood especially the 3 and or 4 way connectors.

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84 300D, 82 Volvo 244Gl Diesel