ABS Weirdness

[gholton@us.ibm.com]

I've never owned an Audi before, but recently bought a 1987 5000 CS TQ for
my daughter, which I'm in the process of fixing up.  When I bought it, the
ABS
would engage at the end of a normal stop, when rolling about 5 MPH.  The
previous owner said that the wheel speed sensors needed to be aligned and
gave me a set of plastic caps to do the job.  After installing 3 of the 4
caps, I
needed to drive the car and noticed that the symptoms that I'd had before
were
gone, but the ABS OFF light kept coming on.  It would stay off for a minute
or
two after cycling the switch off/on, them come back on.  That tells me that
the
ABS computer thinks it knows whether the system is sick or well.  After
aligning the 4th
wheel sensor, the light stayed off, jitters still gone, but the system
doesn't seem
to be working.  When I stop on a slick surface, I get skidding and there
seems to be
no differencein behavior with the system switched on vs. off.   Is there a
sensitivity
adjustment somewhere?  Any ideas?