I'm not really sure how to describe the "hiccup" that my 2008 Fit Sport (115k) miles is making. It's still got pep. Hit the gas, it goes. No issue on the highway, but there's an occasional "hiccup" with the engine. I see the RPMs sort of drop a touch then come back up to normal. I'm guessing its a misfire, but I can't be sure.

Here's some more information. At first, it only happened with the AC running. At the recommendation of a gearhead coworker, he asked when this started happening and it lined up with going to an off-brand gas station. He's thinking bad gas. But in some sort of gas treatment: Mercury Quickclean and the problem went away. Maybe it was bad gas? Next time I filled up, I went with 93 instead of 87. After that tank, I went with 87 at a brand gas station (Exxon, Sunoco, etc). About a day later, back to that hiccup.

So, it seems like lower octane is somehow causing what I think is a misfire but I'm describing it as a hiccup. I'm guessing the solution isn't "just use 93!" There's an underlying problem. Another thing I'd like to note: the car has its original spark plugs still. Is it something as simple as that? Would that cause this issue where it misfires(?) with lower octane gas?

 

On A/T equipped car it feels like a jolt when holding car with brakes in drive. This typically happens when the spark made by high voltage part of the coil goes to the wrong place. I vote for misfire.

 

It DOES happen with the car in drive and idling with the brakes engaged. It however, does happen when moving as well. I need spark plugs or the wire?

 

You need four ignition coils and the spark plugs

 

Sounds like your spark plug gap may have opened too wide from wear. If you haven’t adjusted them lately, try doing so.
The specs for the GD3 is .044” to .051” IIRC, but I feel that even .044” is too wide. I might try .032” and see if that helps. FYI, I am using Denso IK22s, set at .028” and it runs great. You may loose a bit of fuel Mileage, but it might cure your hiccups.

 

Thankfully smog inspection is not checking for spark plug modification