I have an 08 Fit sitting around 130k miles. The thing can't seem to go more than a few months without developing another misfire at idle. In the past ~20k miles I've adjusted the valves, replaced the spark plugs, and replaced the ignition coils. It started up again a few weeks ago, so I took it to the dealer this time. They updated the PCM and told me it was fixed, and it definitely got better. But after a fairly long drive, maybe half an hour+, I still get the occasional hiccup while idling. Never while the car is cold. No check engine light, doubt a mechanic would take the time to diagnose it yet. I seem to have burned through the usual suspects already, so I'm coming to you guys for help. Does this sound familiar to anyone? This car is making me dread stoplights like I never thought possible.

 

Very familiar. What is the name brand of coils and where did you purchase them?
Same for the plugs.
Did you use anti seize/ dielectric grease (you should not!)
I am leaning toward counterfeit coils...

 

Missfire, if you have installed the correct spark plugs, used quality coils, and have the valves adjusted correctly, then you should typically be ok 6 months later. I usually go ~75,000 miles between valve adjustments.
I would suspect that your spark plug gap has widened, and needs to be addressed. Honda recommends a 0.044”-0.051” gap. I personally felt those specs were too wide.
In 2007, I experimented with gap spacing, and found that if I gap my plugs at 0.035” the misfires would disappear.
Give this a try before spending any more money. If you are lucky, this might be all you need to do!
If that doesn’t help, maybe try a quality fuel injector cleaner.