Italiaspeed had this to say about the diesel engine at launch:
"Alfa Romeo 2.0 Litre JTDM Engine, 170 HP and 360 Nm (Euro 5)
The 2.0 litre 170 HP JTDM engine (Euro 5) is a natural development of the 1.9 liter JTDM engine from the point of view of both performance (with an increase in torque and power) and emissions, satisfying the limits of the Euro 5 directive and achieving CO2 emission values (in the combined cycle) of a minimum of 136 g/km and a maximum of 142 g/km for the Alfa Romeo 159 (sedan).
The increase in cylinder capacity has been obtained by increasing the bore from 82 mm to 83 mm: this solution, together with a new variable geometry turbocharger, positions this engine at the top of the market. And with a reduction in fuel consumption: for example, the Alfa 159 Sedan in the combined cycle recorded 5.4 litres/100 km. In addition, the compression ratio is reduced from 17.5:1 to 16.5:1 (giving a consistent reduction in NOx) while, compared with the 1.9 litre JTDM engine, the new engine uses a “low voltage” glow plug which allows starting with minimum preheating times. Last but not least, compliance with Euro 5 emission limits is ensured by the use of a close-coupled diesel particulate filter (CCDPF) and an advanced exhaust recirculation system (EGR), in which all the sub-components are packed into one small component (the EGR module).
Finally, on the Alfa 159, a special equipment package is available (green tires, modified gear ratios, etc.) further reducing fuel consumption and emissions of CO2 without penalizing the driving pleasure and sportiness typical of the brand, in respect of both the 2.0 litre 170 HP JTDM engine and the 1.9 litre 120 HP JTDM engine. The values obtained (respectively 136 g/km and 138 g/km on the Alfa 159 sedan version) result in car tax benefits in the main European markets where taxation is based on CO2 emissions (for example France, Belgium, Holland and the UK)."
In the FPT road map last year, it was announced that the 1750 TBi would eventually get 230 bhp
"The highest stage of tune, meanwhile, is reserved for the Brera and Spider. Launched at Geneva in 2005 and 2006 respectively, these cars have suffered from poor performance, due to a combination of hefty kerb weight and poor characteristics offered from the GM-derived JTS engines. Alfa has therefore elected to address these criticisms and will launch the 1.8 in a third specification during the year, cranking out 230bhp at 5750rpm and 350Nm from 1750rpm. This will enable the Brera and Spider to achieve a top speed of around 235-240km/h, with 0-100km/h coming up in approximately 7.2-7.5 seconds and combined fuel consumption of between 8.5-8.8l per 100km."
Perhaps even more interesting is that FPT have been testing a 3.0 litre V6 Multijet 2 diesel - now that would make a 159 sing! Maybe this is for Guilia rather than 159?