MD-83
Aircraft Equipment Problem Critical
General Maintenance Action
Aircraft; Procedure; Human Factors
During descent we input left rudder trim. When we released the trim knob the trim knob started to slowly turn back to the right removing the trim that we had input.  We tried a second time to input the trim and the trim again moved back on its own.   We decided to leave the trim in its last position; notified maintenance and landed. Maintenance personnel lubed part of the trim system and cleared the logbook. [On the subsequent flight] during descent; we had the same problem with the rudder trim.   After landing; I called [Maintenance Control] and informed them of the problem.  The aircraft remained out of service for an extended period of time
Following a write up for a rudder trim problem; maintenance was performed and the aircraft was returned to service.  Unfortunately the problem was not fixed and the flight crew experienced the same problem into the next station; where the aircraft was held from service.