The transmission on my '90 v8q has apparently gone into limp mode
(it was fine when shut off one evening, and next morning wouldn't
go into any forward gear other than 3). Display on dash would be unlit in d and 3 and sometimes 1, fully lit otherwise ... But went on and off when driving. I tried to get a fault code and got 2111, which suggests a problem with the rpm sensor. Is it possible for a faulty rpm sensor or connection (to something) to kick the car into limp mode? If so, could someone please tell me where to find this sensor?

 

JWS-
I bought a CD copy of the dealer service manual on Ebay and thought I'd try it out on your problem. I'll try to answer your questions one at a time.
1. You are describing the limp home mode
2. The following can result in triggering the limp mode-
1111 Control Unit Defective
1113,1121,1123,1131,1133 Solenoid Valves 1-5
1231 Speed Sender
1314 Multifunction switch
2234 Power Supply
3221 Switch for Reverse
2122 No Speed
2212 Throttle-valve Potentiometer
2243 Fuel Consumption Signal
2314 Engine/Transmission Electrical Connection
3. I can not find a fault code 2111
4. The books assume you have access to a VAG 1551 Diagnosis tester.
5. If you can not get the VAG 1551 Diagnosis tester to work, it should be possible to count the flashes on the dash. There are four sets of flashes. If there was no fuel consumption signal, it would flash like this... flash-flash flash-flash flash-flash-flash-flash flash-flash-flash (2243)
6.The RPM sensor is inside the transmission. You have to lower the transmission until the 8-pin plug is accessible. Then check the wires of the 8-pin plug with the US1119 tester.

I am going to assume that you do not have access to the testing equipment required and could not go any further. You can, however, use this info to direct your mechanic and make sure he doesn't go on any wild goose chases.

Many Thanks
Jim
90 Audi V8 Quattro