Auto transmission bad behaviour

[LeRich]

My 75 is a facelift 1.8T auto. It's done 57k and has been well looked after.

I bought the car October last year and have found the behaviour of the transmission getting worse since. The symptoms:

• Occasional aggressive (thumpy) up-changes
• Very occasional reluctance to up-change
• OTT engine braking on downhill sections
• Not changing down/disengaging when coming to a halt (seems to change down through all gears in quick succession)
• Fighting against the gearbox drive when decelerating
• Thumping when shifting from Park in Reverse and into Drive.

The car was T4'd just after I got the car (on 47k) and was given a clean bill of health (all the solenoids were fine). I changed the gearbox fluid in the summer and noticed only a very mild improvement afterwards. Pulling the fuse or carrying out a battery disconnection reset temporarily improves things. Selecting 'Winter' mode improves matters considerably. These factors show the mechanical elements of the gearbox are not at fault and that it's an electrical issue.

The gearbox ECU is located next to the fuseboard behind the glovebox. To obtain the part number from the ECU (there are many different variants) I removed the ECU, disconnecting the multiplug. Once the PN was retrieved, it was reconnected and put back together. The test drive afterwards revealed a transformed car, with the transmission's behaviour improved considerably. Theory proved. Since that time, the ECU is relearning its bad behaviour and the symptoms above are returning.

So my question: as it seems my auto ECU is at fault, can they be swapped without being mated to the car? I have obtained another ECU removed from another 2004 1.8T but am reluctant to swap in case I cause some sort of network conflict in the car and render it undriveable. Any comments?