When i first got my allroad a few years ago the best i got was 530miles (36mpg combined) to a tank of ordinary diesel. She would start almost telepathically as soon as i turned the key and I would lug the engine everywhere keeping the engine in max torque band (1800rpm). Car came with genuine Audi cams, AKE turbo, etc.
After various garages have had their evil way with her after having the top end re-built with aftermarket cams, etc, dynamic tuning way out, Castrol 5w40 TDI Edge, 2-stroke oil in fuel, cleaned intakes, genuine MAF, engine flush, new air/oil/fuel filter, reconditioned injectors, *S model turbo, new coolant temperature sensor (green), new thermostat, new water pump, 75w90 (??) gearbox and diff lube i average around 430-ish miles to a tank (combined 28.8mpg). Only a slight haze when i mash the accelerator.
I don't lug the engine as much (bad for oil pressure and oil starvation) and i'm convinced the cams are the wrong profile, turbo isn't right and the pump timing is still out. It doesn't start as ferociously as it used to and seems to run out of puff above 3500rpm. Lots still to sort out. Hope to pull the heads off, port and match to gaskets, etc. genuine cams, bigger turbo with bigger nozzles, re-map and see what happens (with Chris' help of course).