I bought a 1998 UK spec 2.8 30V A8 five years ago in Cyprus. It was my sixth Audi but the last. The car has never run properly and nobody here can fix it. For example it has an irritating fluffy misfire at low speed and low power between 1200 and 2000rpm, pulling gently it does not fire cleanly and you can feel it throughout the car, it varies in intensity and has better days but is generally worse cold. Audi admitted at first the car has a problem and have tried changing everything including injectors, coils, leads, oxygen sensors etc. they even changed the ECU but it remains the same, they even flew a technician from Germany who initially agreed there was a problem with my car but when he could not fix it they all suddenly closed ranks on me and Audi said (in writing) the car was in spec and that if I did no like it go buy another car! The car still has the fault and I have to live with it for now. My first question is "has anyone else had experience of this fault and what did they do to fix it?"
Second problem, the gear selection indicator (PND2345) on the dash lights up as if everything is selected, the transmission works perfectly but you cant see what speed you are in. It might be like this for a while and then next time you start up it goes back to normal until and stays OK until you start up again. Audi did a diagnostic and it said it was a problem with the brake stop switches, they changed these but it is the same. I have now taken the car to another specialist and the diagnostics still say there is a problem with the stop switch and that the power is low on terminal 33. We now think there is a problem in the GCU. My second question is "has anyone had experience of this problem and how did they fix it" and please don't say to change the GCU because there are only three of these cars in Cyprus and no spares.
Third problem, the cruise control has never worked properly which might just be related to the second problem. I have always been able to set cruise control but the restore, increase and decrease speed functions have never worked. I tolerated it as it was but after Audi had tried to fix the gear selection display problem the cruise control stopped working altogether. Audi said it was the switch and changed it but it still does not work at all. Again I have taken the car to another specialist but we have come up against a crazy problem, we cant find the cruise control in the diagnostics! It does not appear in the engine or gearbox control units and we don't see it anywhere else so third question "does anyone have experience of using diagnostics with the cruise control and specifically this failure problem".
As a general observation it seems to me that the diagnostics on this car are well below the standard I would expect on a car like this and for the record I am into damage limitation with this car, I have taken Audis advice and bought a Subaru 3.0 H6 Outback and all I want to do with the Audi is get it working well enough to sell it.

 

1;I would disconnect every connection you can find under the hood one by one and clean it with a contact cleaner spray. "has better days but is generally worse cold" makes me believe there is a contact problem.
2;Sort circuit in the brake light system/ switch can cause transmission problems(TC always open). Faulty or misaligned F125 transmission range switch can cause PRND432 illuminated limp mode. There is a switch on the left side of the transmission. The shifter cable is connected to this switch. There is an adjustment point on the cable. Put the car in P and loosen the adjuster to see if there is a tension in the cable(misaligned). You can check the switch with vag-com. Check and see if the right side mirror tilts down in reverse. (mirror switch set to right mirror). If it doesn't you need a new switch.
3; The cruise control only works if the F125 switch is fine.

 

...to start your diagnostic, the code pops up. I've had to correct the mechanics at the dealer and at an independent shop when they told me I had to replace the switch. If you put you foot on the brake, then turn the key, then run the diagnostic again, it shouldnt pop up. If it still pops up, then read tozo's post again.