[Vwdiesel] morning flatulence

[rOLf peCHUkas]

got to watch the tire guy start up my van today and drive it in to his 
shop
puff of black smoke on startup (then clear exhaust after that - it's 
always clear when it's running and I check it - although I've never 
followed it up a hill)
question: how bad is that black puff? what does it consist of? (it does 
not smell particularly good)
suspicion: may be caused by no GP cycling
when engine is warm but not hot GP circuit doesn't engage and start is 
not instant
black stuff = unburnt/poorly burnt fuel? like creosote from a woodstove?
haven't observed exhaust from a cold startup (will tomorrow) but w/ 
full GP cycle, start is chick-vroom - I suspect black exhaust is less
thoughts?
thanks
Rolf
Cambridge, MA