That's a turbo timer. Since most turbos share the same oil as
the engine, the purpose of the turbo timer is to keep the oil
circulating in the engine and around the turbo bearings for some
time, allowing it to cool more, especially if the car had been
driven hard. Otherwise the oil, especially if it's mineral or
semi-synthetic form, will coagulate and coke, leading to premature
turbo failure.
But that's not what I'm asking..... I don't understand how letting
the engine idle will "burn the excess fuel away"?
