Why is there white smoke coming out of my rear exhaust?

I have  C5 LS1 The car started idling hard last night when I left work. I noticed an odd
order, not like gas, like acetone?  The engine never really smoothed out , but I was in
a residential neighborhood and did not get above 25mph. Within a couple of minutes
the engine light went on and shortly after that white smoke came out out of the rear
exhaust. When I turned the car off white smoke continued to slowly come out of the
rear exhaust, majority on the left side. Checked oil, looks clean and level is good.
Only use Chevron Supreme at the same station, I don't think I got a lesser, but any
thing is possible. The car is not driven hard, but regularly. 85,000 miles on her.
Thanks for your help.