Thanks for coming back to me.
There were no warning lights on the dash when we test drove but the seller said there HAD been one, which was why he was getting this CO2 part replaced.
I didnt notice any excess smoke coming from the car.
Mileage is 39k and has a full Audi service history...although i dont know why the previous owner didnt then sell to Audi and chose a small time garage instead...seems a bit odd to me! :)
Thank you for such a detailed reply.
Just to clairfy, in your opinion, could the P0400 EGR issue potentially be causing the lack or power/struggle from the car?
I will still however get an independant inspecation on it before any funds are exchanged.