Fuel consumption will vary with temperature and fuel quality (bio-blend and cetane levels). With just over 1k miles on the car, my consumption increased also. This is normal for my Mercedes BlueTec and TDI's I have owned in the past. In the winter, more cold starts, more idle time, even more city driving will impact the results. When the weather gets above 72 F, it's normal to see extremely good numbers (see below).
Driving style is imperative. Don't be a light foot off the line. When at cruising speed, keep momentum by using ACC if you have it or keep your foot planted on the pedal and let the car do it's fuel restriction on downhill runs. The real-time consumption indicator is a good screen to keep in the instrument cluster.
The roughness in the idle is either a DPF burn in progress (slightly higher rpms) or a heat-cycle. The new EGR design and the start-stop feature are probably forcing an artificial load on the engine to increase operating temp as quickly as possible. I've noticed three different idle positions so far, the high and low idles are smooth, and the middle idle happens at random times and hovers near 900 rpm. I'd say it's rough to the ears - it sounds rough but doesn't feel rough. Open the door during that "rough" idle and the harmonics change drastically, which leads me to believe it's a DPF burn.
If an injector failed, it would be hard to start. Since the injectors are electronic, you'd also get a few fault codes.
My Fuelly shows the full effect of winter vs summer:
- 30,723 miles logged (55.8 best tank)
- 7,052 miles logged (48.5 best tank)
1,020 miles logged (35.1 best tank)
- 32,911 miles logged (34.2 best tank)