Light smoke when engine runs warm on 1998 Lexus LS400

I have noticed that on two occasions, wispy trails of smoke wafting from both sides of the car. The second time it happened, I was in heavy traffic on the freeway. This afternoon, when I returned to my home, I could smell the acrid stench of burning, although there were no visible signs of burning. Shoudl I be concerned, and what precautions need I take?
Thank you.

Asked by for the 1998 Lexus LS400
Sounds like a leaking head gasket...pumping oil out of the engine? Notice any need to add oil in 1000 miles?