“Weird, floating feelings” are not the summum bonum, as you obviously know. Indeed the Fathers stress that feelings as such, of whatever kind or modality, are at best irrelevant, and sometimes dangerous. It’s a mistake in any case to put too much stock in them or to become concerned about seeking an encore when we have had a particularly pleasant few moments of prayer.
Self-mastery, and then self-transcendence, is the goal, and the use of a prayer of the heart like the Jesus Prayer can help us draw closer to this goal, or these goals, by providing a sacred or sacramental “center of gravity”, and thus a place to return to—often several times within the space of five seconds—when we catch ourselves wandering away in pursuit of some trivial thought or impure emotion. For this effort to bear lasting fruits, however, something other than a car ride is needed. Not that you can’t pray when you’re driving—it’s certainly safer than “texting”!—but all the other subliminal operations needed to keep from having a wreck can’t help but get in the way of the “cardiac concentration” which a prayer of this kind at once presupposes and fosters.
I’m reminded of the story about the two monks who were smokers and who went to the abbot to talk about their problem. “Can I pray while I’m smoking?” the first monk asked, and was told yes. “Can I smoke while I’m praying?” asked the second, but he was told no! Subtle creatures, these abbots.