an easy test for a bad turbo is to remove the large line connected to the air box to the compressor side of turbo. if there is any play in the compressor wheel then your turbo is shot and the likely source of oil to your exhaust. remove the air box, pull the turbo and have a specialist evaluate the turbo (wheels may be ground and out of balance) and decide to rebuild and/or replace it.

I had nasty smelling white smoke (remember synthetic oil smells different - nasty, not sweet like coolant) coming out my exhaust and was able to repair the A4.

A sludged oil strainer starved the engine (and cooked the turbo). after replacing the oil strainer, turbo, oil feed lines.. etc., the smoke cleared the exhaust after driving for 15 minutes.

Car now runs fine (OK, the car historically blows coils in the number #2 cyl., but that's a symptom caused by a separate problem I trying to identify). Good luck!

if that were the case.. why only have smoke on idle and why only sometimes??

have u looked around ur engine compartment to see if u can see any white crust or crud near the tranmission. towards the back of the motor near the firewall and cat. GEt a flashlight and look down in that area. if u see crust u have leaks .

I would check the spark plugs to see if they show signs of coolant. if all show coolant ( wet or sometimes greayish specks) probably turbo. If only one or two show signs then probably head gasket or crack in block or head. it may be possible that the turbo may leak coolant on the exhaust side only thus coolant would only get into the exhaust.