Saab: White smoke, head gasket, white smoke

Question
What is possible problem with white smoke coming from tailpipe at idling and slow city driving? Once on the higway the smoke goes away. However, sometimes the 99 Saab 9-3 convertible does sputtered unti I get to abot 50mph. Help!!!!!!!

Answer
Dwayne:
 White smoke of the nature described usually signifies that coolant is somehow migrating into the combustion areas of the engine...most frequently caused by a failing head gasket. The "sputtering" further reinforces this possibility.Unfortunately it will only progress for the worse with time, so it should be attended to.