scenic II 1.9dci black smoke/ lack of power

I've just bought a very cheap 55 plate scenic, the seller told me it needs a turbo. It drove home with no problem other than lots of black smoke and a lack of power... The smoke smells like the cars being very over fueled rather than burning oil. I've only had a very quick look at the car but diagnostics are showing nothing other than fuel temp at -40, can anyone tell me where the sensor is ? I'm thinking once thats been changed next things to look at would be egr valve, air flow sensor etc? Has anyone changed a turbo btw (how fiddly a job is it ?)
Thanks in advance :)

scenic II 1.9dci black smoke/ lack of power