One problem related to suspension torsion bar has been reported for the 1999 Toyota 4Runner. The most recently reported issues are listed below.
Frame snapped at the drivers rear torsion bar due to frame rusting from the inside. I just had this checked and a little rust to the frame was apparent because it is rusting from the inside and not so apparent. Once it began to decay it just became mostly rust damaged beyond repair and replacement of frame only option. Contacted Toyota and was told there is no help on this model (4runner) but is on other truck models, same frames same year. .