puff of smoke

What is your question?

when I first start the car,I see a puff of smoke out the tailpipe. Car has 126,000 on it. It doesn't do it every time,but it has the past two mornings. The idle goes up as it is supposed to,and pouf of smoke comes out. It goes away instantly. What could be the cause of this? I just wrote about my high idle,and got great answers from pushrod and another master mechanic,and am hoping they can give me another good answer to this. Just changed the oil and filter,use synthetic mobile 1 5/30W. That is what we were told previous owner used and we were told once you use synthetic you must stay with it. It has done this since we got it and before the oil change so you know. Don't want to confuse the issue if I can help it. thanks for your previous replys and I look forward to a reply on this.