Had a similar problem before.
Mine turned out to be the front speed sensor.
I had knocked the connection to it just enough to disturb the signal.
Cleanin the contact up got everything working again for me.
Check the front vehicle speed sensor connection - maybe get some sandpaper and clean up the terminal (about 1" in front of the gear oil dipstick where the heater core hoses go into the firewall. )
http://www.subaru-svx.net/forum/show...ht=speedometer