I have driven this 1990 3,6. for two months. It is a very pleasant car, a challenge to own, a pleasuse to drive.
My problem is that the gearbox computer is set in notbetrieb. only 3rd gear.
Anyone out there who has experienced problems like this?
What kind of sensors is likely to fail?
Is the problem internal?

Hallo/Hej!

The transmission seems to be in fault mode, disconnect the battery to reset transmission ECU (minimum 5min). If it not works drive to Audi workshop for reading out the faultcodes for transmission. Check transmission oil level, special oildipstick required.
(Audi V8 automatic transmission stays in 4 gear if a fault is detected, after ignition is turned off and on the transmission stays in 3 gear).