Speedometer dial stopped moving or it bobs around from 5-20 mph. Odometer works

What is your question?

Only the dash gauge doesn’t display speed. Odometer works fine, both mileage and trip mileage seem accurate. All other dashboard displays work perfectly. Q. How to trouble shoot?

What makes this problem better or worse?

Needle has rested at 0mph for 1.5 years but in last two weeks began fluctuations from 5-20mph. Erratic, dial doesn’t remain stationary.

How long has your 1993 Saab 9000 had this problem?

1.5 yrs. All other dash gauges work perfectly.