It's pretty normal for cars to let out vapor on startup. Especially older, less emissions-regulated cars. (I believe it has to do with water condensation in the exhaust system.) I know mine does if she's sat for awhile.
Not sure if this has any bearing on your situation, but mine used to put out more vapor from one side of the exhaust until I did some tuning and sealed the headers really well.
Now I have much more balanced vapor... when I get it.