Hi, I have a 1997 A6 2.5TDI Quattro Avante. There are a few things that i need help with so any suggestions would be much appreciated!!!

1) Soon after I brought it over from Andorra to Ireland, the exhaust started smoking very heavily. I brought it to an Audi garage and the best they could come up with was that sometimes diesels smoke! In all my ignorance I somehow managed to fix this by bypassing the stock air intake and fitting one of those cone airfilters directly to the engine. NOBODY has been able to explain how this stopped the smoke! Any tips on a good intake?

2) The background light on the small led computer screen is broken and when I asked them to fix it in the garage they said it would cost too much. Any ideas?? Same problem with the battery meter, clock, some heat gauge to the right of the dashboard. Also the light where the air vent controls are broken so at night i cant see where the air is blowing and how hard!

3) Any basic tips on improving engine performance?

Looking forward to some help!