trip computer weirdness

[jos1 at cornell.edu]

Has anyone else had their trip computer suddenly become flaky? On my 
1990 200q, the trip computer just started quadrupling my MPG -- went 
from showing the usual 22-27 MPG under normal driving conditions, to 
102-180 MPG; tank to empty likewise now reads 2000 mi. at fillup, and 
fuel used barely registers. Other functions such as boost, time elapsed 
and MPH are normal.

Any BTDT on what's happening and how I can fix this? The computer used 
to be about 12% optimistic before, but this is ridiculous!

Thanks in advance for any insights!

JS