Consider yourself lucky to have a manual tranny, the rest of us have to get out and use the under-hood panic shutdown lever. The problem is vacuum related and is caused by a leaky component in the vacuum system or a malfunctioning part in the vacuum operated engine shut-off system. Use the search function on the forum and read, read, read. Usually not too expensive to fix, but can affect tranny and door lock operation until its done.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150