Audi a3 tdi. Juddering misfire and hestitation. Abs eml steering and esp light

Hi all. 

Having a bit of a nightmare with my Audi a3 at the moment.

So last week my steering light abs and traction light came on. I diagnosed this and I got a code for a rear right abs sensor. I replaced this and did the reset to no avail.

Now a more pressing issue is that a judder has developed. It appears that I have a misfire and the symptoms are as follows.

When cold the car is stable and revs fine. As soon as it cracks a line on the temperature gauge it starts to run lumpy and the misfire appears.

Mpg is poor black smoke appears when the car is lumpy. 

I could do with some professional help. I'm happy to fault find and even more happy to pay someone or buy a beer etc for someone to come and help with vcds etc.

A full service has been done on the car including fuel filter.

Based in Lancashire