Happiness is a throttle that snaps back to idle...i hear ya. A properly rigged and routed throttle cable should do that providing their is no damage in the circuit. Is the cable guide (#17) installed correctly or is it worn? Order a new one if it's effed. Properly installed that white plastic thingy does not really require lube as already suggested as that will only attract dust and dirt and make it worse in the end. Only the cable ends need a touch of lube. Are the 2 throttle housing halves lined up to the punch marks on the OEM handlebars. If not OEM bars then rotate as req'd until their is no friction and cables are at their slackest and not tight and stretched. Order a new tube and grip from Honda (#12) if worn. Patience and persistance...keep fiddleing in the grip area and you will solve it. Obviously with those cables disconnected it sounds like you have already eliminated the cable run/conduits/spring.