2002 x5 3.0L petrol

[Rob Faure]

Morning all ,
My X5 has an occasional asthma attack!! Occasionally when driving there is a huge cloud of white smoke that comes out of the exhaust- resembles an atomic bomb! Poor cars behind are terrified...
I have read various posts and I dont think it is coolant or oil, car not using either oil nor coolant. There are no codes present on the dash and the car stops smoking and runs clean again.
The car is also heavy on fuel and lacks power.
Could this be injectors? I kind of ruled this out as is only happens occasionally.
If it is a vacuum leak the car should use oil due to a faulty cvv valve - the 'smoke' is white but there is no burning oil smell. No fuel smell from the sump.
I am no scientist so any ideas before I send the car to a clever person !!