It looks like I'm the pioneer on this one. I noticed the other day that it took a couple of extra seconds to shut down and then, when I came out of the store...hard to start. So, I went on to my next stop and this time I opened the hood and used the stop lever to shut off the motor just to see what would happen. BINGO! Car started perfectly. Going to replace the vacuum shut-off valve tomorrow! I amaze myself sometimes!
As far as the rough idling, I probably will still replace the fuel filters as well.

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1982 300D Turbo "Helga"
380,000 miles