Shuddering/missing when at operating temp

[k.trazy]

I have a '12 2.0 SkyActiv-G w/6MT, when up to operating temperature and coming to a stop light/sign and at 0mph, my engine seems to be rough/shuddering intermittently. No CEL or the MIL (wrench icon) in the middle of the instrument cluster came on. Compression ratio maybe low in one of the cylinder banks? I know the SkyActiv-G has a 12:1 compression ratio, so if it's slightly off, that can certainly do the shuddering/missing but should throw a CEL or MIL.

Thoughts?

 

[dmention7]

Are you talking rough and shuddering like it feels like it's going to shut off, or just that you can momentarily feel some vibration where the engine is normally perfectly smooth? If it's a fairly severe shuddering, it could be something like a vacuum leak or a sensor on the fritz. If it's just a slight vibration, that could be varying load on the alternator causing a momentary drop in idle speed.

If it happens consistently or every time you come to a stop, I'd just bring it to a dealer and let them worry about it. If it's very intermittent, maybe borrow a code reader and see if you have any codes pending... but in either case, it's not likely to be anything serious, especially with no codes thrown yet.

EDIT: also regarding compression ratio... about the only thing that can change the CR without disassembling the engine is putting in the wrong size spark plugs. Even then, you'd notice that under heavy load, not at idle.

 

[k.trazy]

Hmm. Interesting. It's slight shuddering/missing when coming back to idle. Usually when coming back to idle the engine is perfectly smooth but on occasions it would come to an idle that feels off.

 

[niterydr]

Doesn't the sky-activ technology shut off at a stop to conserve fuel?

 

[k.trazy]

Not that I'm aware. It hasn't auto-stopped for me before. Usually though if it auto-stops, it would flash "AUTO STOP" and have the tach go to 0rpm.. At least that's what my buddy's Civic Hybrid works.