Try checking the ignition control module. You could try swapping your ignition control module for another one which is in good working condition, and if the problem is gone, then you know where the fault lies. My module has given me problems of intermittent stalls, and before I changed it, my idle RPM at N or P was around 1200-1300. My new module gives me 900.
And of course get your mechanic to adjust the timing too. Lastly, make sure your plugs are copper ones, not platinums. The latter gives some hesitation and stumbling especially during idle.