Eric,

I don't have to let it set to cool down.  Just switching off the ignition and
starting it right back up makes it run fine.  Then, after maybe a minute or two,
the rough running starts to occur again.  I can then switch it off, and back on
and the cycle will repeat.  Like something is resetting when the ignition is
switched off, and then  builds back up again, to make the engine misfire, black
smoke, no power, poor running.  I finally had to stop at a friends place ( VW
Mechanic), and take the bus home.  We are planning to diagnose it later this
week. Just trying now to determine what we think it might be.

Thanks,

Charles