Had the car now a good few weeks but not sure if its developed one or more faults or if they are related.
symptoms, when they occur are:

sometimes coil light flashes - idling at tick over
Temp stays at cold but then jumps up slightly but never to normal

Have had the car serviced and since done a 900 mile journey in 2 days - had a strange problem as i ran into loads of spray from lorries on the motorway, lost the kickdown acceleration - not sure if its related or not, soon came back after about 5 miles as it dried out.

The work that has been done on the car so far is, replace the engine oil and filter, replace the automatic transmission fluid and filter, replace the diesel heater plugs, when the plastic engine cover was removed the soundproofing was falling apart so was removed but the plastic cover was replaced.

My train of thought - cheapest first - was to change the temp sender/sensor then change the MAF unit

Tried putting injector fluid in tank which initially improved things but went back to normal - MPG isn't too good (about 30mpg)

Its a 1.9TDi Diesel 1999 estate A4 B5 AFN engine - 179k miles

NO warning lights appear on the dashboard and the way i have found to stop the coil light flashing is to allow at least 10 seconds for the heater plugs, start the car and hold the revs higher than normal, if the coil light doesn't flash then it won't flash at all till i restart and sometimes not, so very intermittent.

 

Sorry to inform you but you probably won't find much help on here. We unfortunately don't have diesel B5 A4's in the US.