Are you on about freeing up a sticking turbo?
My 07 plate Audi A6 TDI had this problem, treated it to a bottle of STP Turbo Cleaner, , which I was sceptical about, but had nothing to lose, after 50 or so miles, the turbo was functioning properly, and did so for the next 13k before i sold the car earlier this year... and would like to think its still going strong!
Thom