My 1994 A6 2.5 TDi 5 cyl with it's poor cold starting (see earlier thread) had bee diagnosed by main dealer as requiring a new engine management unit (£1400 + VAT - ouch).
They have made a fix which disconnects a sensor on the top hose coming out of the head which fools the ECU into thinking it's cold and forces the glow plugs to come on. Starting is much better with this arrangement, but by no means fixed. It also pretty much makes the car un-saleable.
Any ideas where I can get a replacement unit without remortgaging the house?