I had a similar issue in my 2.4 (mapped with no DPF or EGR). Some research on these forums pointed me towards an injector fault as it seems that the direct injection diesels shudder/misfire/chug at low rpm when the injectors are missing slightly.
The fix is easy and cheap though so don't panic!!
1) Buy some electrical contact cleaner from halfords
2) go home and remove the engine cover (just lifts off)
3) disconnect the electrical connections from the injectors (they just unclip)
4) spray a healthy dose of electrical cleaner into the connections on the injectors and the cables
5) do this a few times till your happy they are clean
6) wait for it all to dry and reconnect it.
1) Buy 1x 325ml Wynn's Injector Cleaner For Diesel Engines
2) Buy 1x 500ML Wynn's 12193 High Pressure 3 COMMON RAIL DIESEL FUEL Injector Cleaner
2) Run your vehicle till its on the refill light with limited range
3) add the full bottle of 325ml Wynn's Injector Cleaner to the tank
4) Go have fun - seriously, drive it hard, drive it soft and run it till your about to run out of diesel (don't though, that's a bad thing to do)
5) fill your tank as normal before you run it out of diesel and add the 500ML Wynn's 12193 High Pressure 3 COMMON RAIL DIESEL FUEL Injector Cleaner
The car will be transformed and should no longer be showing the symptoms you had before. If it does you need to go to an Alfa expert and get them to check your injectors. You can repeat this process a few times if you need to see if you just have really, really dirty injectors, before having to buy new ones.
Diesels are heavy oil and get dirty through normal use. This procedure works on any diesel car and literally transforms it for a total investment of around £20