87 5000TQA Anti-Lock Brake Problem

[Leon]

Seems like they may have messed with the speed sensors, maybe one of
the connections got loose and now has an intermittent connection. The
other thing might be that the axle has a different spacing for the
sensors, to pick up the speed from the wheels. Here, have a look at
this site and bookmark it, great reference.
http://www.sjmautotechnik.com/trouble_shooting/brake.html

Good luck,

David