What is wrong when your car is idling and white smoke is coming out of the exaus

How long since last oil change? oil not overfilled? Proper synthetic oil being used?Does it only blow white smoke on cold start -up , or anytime it sits idling for a few minutes and then smokes on initial acceleration?

Is it really bad! Engine running rough? Check your oil if it's mixing with the coolant( chocolate milk) looking fluid

If you scan the forums, you'll see that these cars are known to have defective valve seals. It's an expensive repair if you're not a do it yourselver. Go get it tested and if this is the case, you might want to go to Bimmerfest forum and ask where a good mechanic is located near you that won't rip you off in price. The best price I've seen is $2500(NY/NJ area). I hope this isn't your issue, but if it is, you need it fixed or you'll ruin the engine and the car isn't worth a replacement.