Most common problem with these (in terms of failure) is the speed sensor signal going to the steering computer.
Check there is speed signal going to the steering computer.
In analog/cable type speedo's I believe the conversion to the pulse to be fed to the computer happens in the dash. Not 100% sure.
On another note, are there any Toyota's with this incorporated?
All the models I can think of that had the feature had a seperate computer?
On a probably useless note, my mr2 had inconsistant steering response, and that was a failing alternator. It's electro-hydraulic power steering but, so that probably doesn't help.