1988 Other Subaru Models Intermittent stalls

XT with 2nd engine at 195,000 starts fine, then at a stop, stalls & dies, take a long time to restart. Other times works just fine. Engine light is on, but not a new thing, occasionally goes off. Mechanic says can't check out the engine, since the computer doesn't give any signal. Do I need to replace the engine computer, is that the problem.

Had a recent tune up, the wire harness was replaced, injector line hose clamp was loose and tightened. fuel induction cleaning, clean throttle body, clean idle air passages, perform top engine cleaning, install fuel injector treatment.