I would suggest then, that the throttle pot (now reconnected) has some issues that someone tried to mask by disconnecting it.

That device gives you 3 functions.
Throttle closed (idle) switch
Wide open throttle (full throttle) switch
And
Position/angle potentiometer

A fault in mine caused erratic behaviour at 1600 rpm (I'm sure I wrote about it on this forum)
Check for-
Water ingress into the pot itself
Bad contacts at the connector

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