I am working on a 97 a4.18tqm at the moment.
Every time you start the car, you get 2 dtc errors codes.
One is the Loss of Bat power, same when you disconnect ecu. This should not occure when starting car..
The other error is the idle speed controller.
tried clearing them a number of times, but a soon as you start the car, the errors come back..

Each time you start the car, the current draw from the starter may be causing the constant 12V supply to the engine ECU to drop too low, hence the low power code. Starting the car while the ECU is dropping out will also corrupt the t-body settings, which can result in the idle speed fault. Have you checked t-body adaptation at data block 98? It is probably corrupted.

I was think along those line last night, but it was getting late..
The car has had a after market cruise control fitted, I wonder if some wiring was upset or not installed correctly...