As you all mentioned, I asked the shop to check a number of the items, in particular the wiring harness. By the way, the engine is a 3.2 liter ohc 6-cylinder. To my delight, the wiring all checked out fine. Sparks were replaced, oil fliter, and engine tuning. That seems to have done the trick. I will drive next couple of days to see whether anything changes. Since there were no lights on indicating some failure, it appears the remedy was pretty straightforward.

Don't know if I mentioned, but the car had sat a week at local MB dealer without anyone looking at it so I pulled it out to have work done with the bosche authorized service shop. Where's that focus on service? Anyway, thanks to all. Hope I am not back for awhile.