Hi,

I have a '92 525, 5spd with an electronic speedometer that is going
spastic. It started a year ago as a once in a while thing and has
gradually gotten worse.  The car does not have a limited slip
differential.  I've owned it since new and had all the services done so
it is a well maintained vehicle - if that has any impact on the problem.

The speedo usually works fine for the first 10-15 minutes of driving and
then will start erratically bouncing around, like it's getting voltage
spikes.  It rarely will go below the actual speed.  It'll stop for a
mile or so and then do it again.  If using cruise control, it eventually
gets to the point of being quite annoying as the car then acts as though
it's misfiring. If the car is stopped, it stops and registers 0.  
However if the car moves ever so slightly it will sometimes spike up and
then come to rest at 0 again.

My guess is it's the/a sensing unit.  If any of you agree, can you tell
me, or describe where on the car this unit is located?

Any other thoughts appreciated as well.

Thanks,
Nate