Why does Check engine light keep coming back? on 1997 Saab 900

Vehicle sat one year. Started up first time after replacing all fluids and filters. Uses no oil. Has 180,000 miles. Gets 32 miles to the gallon. Spark plugs pulled. Look fine. Compression tested reported with in specs. Cant find the source of the check engine light after resetting usually comes back within 150 miles.

Asked by for the 1997 Saab 900
Computer trouble code numbers?