1.9 TDI not available for the Touareg. Smallest engine is the R5 2.5 TDI with 174 hp or 128kW. That R5 aint one of the most reliable vw engines and is too big after the modifications to get the engine efficiency over 35% at 100 km/h speed.
20hp at 2000 rpm is 240g/kwh -> 0,24->35% efficiency