what spec? Is it PD or VP turbo-diesel? And what power in kW/bhp...
go to
Chip'n'Spin or
R-Tech
Here's the R-tech track record on remapping the 1.9 TDI's:
Audi A4 1.9l TDI VP stock: 90BHP 210Nm remapped: 118BHP 263Nm
Audi A4 1.9l TDI VP stock:110BHP 235Nm remapped: 146BHP 278Nm
Audi A4 1.9l TDI PD stock:100BHP 250Nm remapped: 130BHP 300Nm
Audi A4 1.9l TDI PD stock:110BHP 235Nm remapped: 140BHP 272Nm
Audi A4 1.9l TDI PD stock:115BHP 285Nm remapped: 145BHP 335Nm
Audi A4 1.9l TDI PD stock:130BHP 285Nm remapped: 160BHP 335Nm
...or
e-mail Mark at Chip n Spin to see when the next rolling road day is.
All of these are around £200-£300 normally (although there are some budget £75 options too, but I'm very wary of those)... and if you wait for a rolling road day, those sort prices can include a before and after rolling road session.
Also, the remaps will usually result in slightly better fuel economy because teh engine is more responsive at lower revs, so you tend to drive in an even higher gear...
Beyond that, you can look at changing injectors and bigger turbo's but that is likely to ruin your fuel economy, insurance premium and also cost a LOT more than a remap!