91 Ford Tempo

I have a 91 Ford Tempo w/2.3 L and 123,000 mi. On occasion I have an engine light that comes on and goes off with no repetitive conditions. Usually by the time that I can get a scan tool on it, the engine light has gone off. I do get a code 10 for snap throttle and code 77 (gooseneck test not run). What do I need to do next? Thanks, Groovyforster