My son's car was having intermittent stalling problems during his first semester of college. I finally was able to troubleshoot what was going on. Apparently Honda had a real problem with their ignition switches during this vintage. There was supposedly even a recall because of this. I also took this opportunity to replace the O2 sensor, which had an open heater circuit and was responding sluggishly. Hopefully the new one will improve his gas mileage.
1999 Honda Civic Ignition Switch Problems.