Thanks for update, I was right about leaking plugs
I bought my plugs (Denso 2 from O'Reilly's and 2 from Napa)
2007 car came with Denso plugs and Mitsumi relays
2008 car has Denso relays as well (Junk yard is a greatest school)
From my experience:
clean spark plug very well using lint free blue napkin sprayed with carb cleaner or equivalent to clean the plug gasket seating surface
use light and mirror to make sure it is "aluminum color"
tighten the plugs by feeling (to flatten the sealing gasket)
Use no anti seize of any kind F the manual telling that!
One of the plugs IMG_3625.jpg shows round gasket meaning it was not crushed
while is possible to get fake plugs from e-bay some dealerships are selling online expired, returned or damaged parts (timing belts is one example)
https://www.denso.com/global/en/prod.../basic/torque/
https://www.densoautoparts.com/spark-plug-installation
the website calls for 15 foot pounds which is very common setting for older engines

 

Bought our 2008 Fit new. Factory installed plugs were NGK Iridium.

I replaced them with Denso IK22's back in 2009 and have been running IK22's ever since. Change them every 50k miles and always use a small dab of anti-seize on the plugs and dielectric grease on the coil boots. I hand tighten them until I feel the gasket get fully crushed and the plug bottoms out. Don't use a torque wrench because I don't really care about the torque value. If 20 ft/lbs doesn't get the gasket crushed, it's not enough. Conversely, if it's fully crushed at 15 ft/lbs, it doesn't need any more torque.

In the end, I don't think it matters which iridium plug (NGK or Denso) you use as long as they aren't fakes and I don't think it matters whether you use anti-seize or not or whether you use 13 ft/lbs or 20 ft/lbs as the torque value as long as you fully crush the washer.

 

Thanks as always, Doctor J!

 

Plugs are in and the car is again running smoothly.

Am going to test the #2 coil pack just to ensure it did get fried / is performing poorly (the car's performance feels a bit down).

Will also be checking the plugs to make sure they're not coming loose when I yank everything for the valve adjustment.

Thanks all!

 

Most likely the boots are discolored and may somewhat deteriorated
Today on Anaheim PYP I saw Fit with relatively recent less than 3 years OEM replacement coils.