'93 90 S vibration

[Jim_Bresee@idx.com]

Howdy,

My '93 90 S (about 78k miles) has a vibration in the front end at speed
(say, 50mph and up).  Actually it's almost more of a wiggle in the steering
wheel.   It is noticeably worse since I put new rubber on the front
(Michelin MXV4's).

The most pronounced wiggle can be reproduced by gently pressing the wheel
slightly out of the center position while driving at speed.  Under braking,
there is not a pulse in the peddle, but I do feel a slight pulse in the
deceleration.

I'm guessing that the problem is a warped rotor, but since Costco will
re-balance the front rubber for free, I thought I'd start there.
I've done work on my cars for years (VW's, American Family Truckster from
Chrysler, etc), but I've never worked on an ABS brake system before.   Is
it more difficult to do a brake job on an Audi 90 than, say, my VW Golf or
Fox?  Any special precautions?

Any thought's on other things I should look at to diagnose the vibration?
Thanks for your collective wisdom!  This is my first Audi... I've owned it
about six months and I love it.

Jim