Audi 80 tdi juddering/ erratic idle
 

I was wondering if anyone can help please. The car is a 1994 M reg 1.9tdi.
It has started to shudder when accelerating in 4th and 5th gear, its like im in too much of an high gear for the engine speed, and when standing at traffic lights, it used to sit on dead 1000rpm but now cannot make its mind up and starts bouncing lower than 1000 rpm. This then makes the car shake, It started about a month ago.
Every time i service the car its genuine parts and the mileage is 166k.
Thanks for any help.

I have also noticed that the exhaust tips have started to soot on the ends, they used to be quite clean