Shame for Robert. I will post more about boost pressure next week, but basically the turbo pressure has to be controlled at low rpm as you can easily go way more than 2.5bar absolute. At high rpm you are limited by the restrictor.
The FIA has got a control box with few sensors connected to it (fuel rail pressure, turbo boost), and there is someone that is dedicated to check all cars during the rally at few points to see if the car didn't trigger any alarm (over boosting for example), but they are generally cool with it as long as you fix the problem quickly. Seems like here this problem stayed for a long time for it hence the penalty.
But now the top 3 is within 5 seconds, it cannot get any closer with 1 stage to go, it is insane! Will Mikkelsen get his first victory? Will Neuville be the only 3rd non-Scandinavian ever to win this rally? Will Ogier win again? 1 hour to go and we'll have the answer!