I've never had any sign of smoke from the car, despite 31/2 years of BPU, but tonight driving home I was coasting in D down a hill, knocked OD off and thought I saw a quick puff of smoke out the back. I then knocked it into 2 and am positive I saw a bigger puff. drove the final 5 mins home knocking it between 2 and D with the odd burst on boost then off then back on throttle, but didn't get any more.
Got home and checked for smoke on idle, but nothing, so went for a 10 min drive and tried to recreate it down the same hill at the same speed etc, but nothing. I let the car cool down and went out again. No smoke on start up or idle and couldn't get it to do it again.
Any ideas??