turn the idle up. (screw on the throttle body.)

due to the plug being white and/or chalky leads me to believe your car isn't getting sufficient fuel pressure and is running super rich (another reason why your car could drop rpms and give you the illusion of poor firing/timing), check you injectors and have them flow tested. if that doesn't work replace your fuel filter and possibly your fuel pump. checking distributor timing also wouldn't hurt. and i doubt it, but you could be running a plugs a tad too cold.

grab some NGK V-powers (BKR5E-11) gap to .39.