nackered turbo?

[willJspears]

So i was sitting in traffic and my car would unexpectedly rev up to about 3000, then calm down to normal, it did this about 4 times, it then made a horrible vibrating noise when i hit boost while chucking out grey smoke, it then revved uncontrolably even when i turned the ignition off, i managed to kill the engine by covering the intake, is the cause of this a blown turbo?