I sometimes see a nasty grey cloud of smoke from the exhaust of my 84.
Digifant EMS on an inline VW motor.   I am guessing it may be a faulty
throttle switch that sometimes goes to 'full rich' for whatever reason.  By
intermittent I mean....When I go to town, perhaps 1 trip of four, this
smoke shows up.   It doesn't smoke at every signal....It may do so for two
in a row, then no smoke at all the rest of the driving around.   It
sometimes even smokes breifly on start up, but very seldom...

  Here are the specifics of how this occurs and when:  It normally happens
in the city when I am stop and go driving or hitting traffic lights.
Everything might be normal without any problem then I will roll up to a
signal and idle there while the light cycles then as I leave, the van puffs
out an embarrassing cloud of grayish exhaust smoke, lasting perhaps two
seconds before the exhaust clears back up and is again invisible.    I have
also noticed that on start up, then coasting down a longer hill the exhaust
will backfire....I do have an air leak in my exhaust system which probably
allows air in to make the loud bang more likely...

   I see no smoke on long hill descents.   Nothing when I redline the motor
to 6000rpm.   I don't burn much oil for a VW inline, but I do have a slight
leak at my homemade filler when I park with the nose up on a steep
incline...a quarter sized puddle below maybe.

   I think my throttle switch is NLA...I think it is the longish leaf
springy looking type...It seems to click correctly with linkage movement
and it clicks off when the throttle is closed...when I do it in the engine
by hand...consistently and correctly..

  Anybody have any other ideas about this stinky cloud of smoke I sometime
see?   I hate puffing that into our air, though it's probably nothing
compared to, say,  a coal fired power plant...a minor 2-second visible
exhaust puff a few times a week...