Audi Repair: 1998 A4 2.8 Quattro auto - rough gear change and stalling after disconnecting battery, brake light switch, fuzzy logic

Question
hi Jan,

A while ago my battery died - after replacing with a new one, my auto gearbox changes gears more roughly than before, and at first did not appear to correctly disenage clutches or unlock  TLC when stopping (i.e there was a noticeable jerk and rise in revs when changing into N when stationary, as though resistance removed). No DTC codes were reported despite numerous scans - eventually I fiddled with the channel 14 adaptation (after trawling the internet for hints0 and improved things - i.e it did not stall. However, I have since had to disconnect the battery again, and the same problem has restarted - slightly jerky or inconsistent gear changing, and the engine sometimes stalls when braking to a stop. Theonly DTC code reported refers to 'brake switch' signal implausible. Is it possible that the gearbox does not recognise that the brakes are being applied, and therfore is not unlocking the TLC in time? Until I can adjust the 'min spec torque' with the work's VAG diag box, I will have to keep changing into N when slowing. When the engine is cold it does not tend to stall - I presume this is because of the increased fuelling rate. increasing the 'increasing/decreasing load' fuel adaptations does not appear to help. I am hoping that the gearbox controller needs to recalibrate, but is there a way to force this? Any help would be much appreciated. Thanks Adam

Answer
The brake light switch is a common failure item.  I would replace it since it will probably fail soon anyway.  With reference to the computer, yes it uses fuzzy logic, where it trains itself as it is used, also the idle control on the engine ECU will do the same thing.  It could be that those things combine to give you the rough running until it settles in.  After about 1 hr running time it should be better, let me know if it does not straighten itself out.  Jan