The car had been running fine after swapping the viscous fan.

I pulled the codes whiich have come up with 2121, throttle switch. I tested it off the car, after cleaning the contacts (some moisture around pins 5 & 6, with verdigris). It appeared to give a good open closed, 0ohm to open circuit result using a decent DVM

85 WR quattro
90 V8 Silver, 91 V8 Black, 93 V8 Lago
93 100e quattro V6. Titan, i think