Elmore Leonard famously said the key to writing well is to "skip the boring parts." This is sound advice. Boring the reader is about the worst thing a writer can do. I also think that writers, with experience, can actually tell when their own writing is boring. In drafting such sections, they feel mildly persecuted, as if their boss has just told them to redo the budget. Similarly, in revising, they find themselves skimming over the same sections their readers will skim. Simply responding to this unease--whether or not you know its source--by cutting out these sections and finding something to replace them with will go a long way toward improving your writing.
But what, in the case of literary fiction specifically, counts as "boring"? I would say it's writing that does not stir emotion. More specifically, readers who read literary fiction seek emotional experiences that are both complex and powerful. This does not mean you need to be punching your unseen interlocutor in the gut at a rate of one hit per second. You want dynamics, as in music, fortes and pianos and everything in between. But it does mean that something emotionally interesting should be going on, virtually at all times.
This idea doesn't line up exactly with "show, don't tell." I believe "telling" (i.e., the well-done summary) can be emotionally satisfying. It also doesn't line up with "action," in the usual sense. Scenes of contemplation, descriptions of settings, and so forth can certainly move your reader. But you might ask yourself these sorts of questions: Is this section doing something, or just reporting something? Is this creating an experience, or is it merely duct tape holding the plot together? Above all: Do I feel anything here?