Puffing grey smoke

Ok, gotta a small question.  My 92 3kgt is puffing grey smoke, not all the time, but usually when cruising, and hit the gas a little, there is comes.  I've noticed it at idle a few times as well.  I had it in the shop, and the mechanics can't find anything wrong, but it still doesn't seem quite right. Power is good, no losses there that I can tell.  Any ideas, should I be worried or is this something that is normal?  Any help is appreciated!  Thanks in advance!!
Rob

Hi, White smoke is burning antifreeze.  Blue smoke is burning oil.  Black smoke is running rich.  I think your catalitic converter is starting to wear out or break down.  I would do nothing, replace it, put in aftermarket stock or performance, or do something creative.  I see no reason to worry, good luck.

Thanks for the advice...I figure with 87k miles on the car, small things will pop up here and there...I'm working on doing the exhaust, new cat...just trying to find the best route to go on that for the buck...