I have a 2014 Porsche Macan 3.0-litre diesel, bought new. It recorded 42mpg or better on a long run and 39mpg average on short urban runs. Porsche wrote asking for the car to have a software update for emissions. I was very suspicious about this and received written assurances from Porsche UK that the fuel consumption would not be affected. But the mpg has fallen dramatically on short runs to 33mpg and on the long runs to 37mpg. I feel duped by such a prestigious company. Is there evidence that a defeat device exists in this particular device as per the Volkswagen situation?