I have a 2015 A6, have been having problems with it recently it initially started with DPF filter light - drove it as suggested by garage in low gear plenty of revs and eventually it went off. Then if I tried to give it any welly the engine management light started to flash and it went into limp mode, eventually stalling and not starting! It also had the most annoying whizzing sound. This happens a number of times, took it back to the garage and they changed fuel pump and cleaned the fuel tank. All good. But now the first start of the day is really slow it eventually starts but it takes a while does anyone have any ideas what it could be.
All help/advice is greatly received
thank you