Changed my spark plugs at 48k miles (total mileage on these plugs is 22k, replaced the coils and wires 22k miles ago as well with BHR's coils).

Carbon deposits look minimal, but its noticeably black on the tips of both rotor 1 and 2's leading plugs. Does this look like a misfire to you? Also, rotor 2's leading plug has a green-ish colored deposit on it as well, I'm not really sure what this is from.

Haven't had any CELs/flashing CEL to indicate a misfire at any time, no hesitation nor has power at high revs noticeably changed. The only thing I have had is what sounds like it could be a misfire while idling (I would describe it as the engine "stumbles" - but idle RPM doesn't waiver nor hunt). Usually these "stumbles" are spaced out by 5 or more seconds, so is it possible it isn't occurring frequently enough to reach the ECU's misfire threshold and trigger a CEL?

Thanks for your input.

 

plugs look okay to me for being used 22,000 miles.
If you're not seeing or feeling hesitation at high rpm's, you might not be misfiring.
when you hear that 'stumble' at idle, does it coincide with the ac condensor cycling?
if not, do you have a timing light lying around? You could connect it to each spark plug wire and see if the coils are firing properly. (this is how I found out I had 2 bad BHR coils a few years back)



p.s. what's up with nude mice literature?

 

I've never had the engine "stumble" when the AC was on (most likely because I rarely use the AC). I don't have a timing light, but I will see if anyone I know has one that I can use for a day to test out the coils.



I was trying to get a good picture with the spark plugs' tips in focus, and didn't even notice the nude mice article until you pointed it out

 

check with Auto Zone, that might be one of the tools that you can rent / borrow.

 

ESS and MAF sensors were cleared, and the NVRAM reset 22k miles ago when I changed the coils/plugs/wires. They were cleaned periodically thereafter. Most recently they were cleaned and NVRAM reset at the 40k mile mark. Cleaning and then resetting the NVRAM did not make a noticeable difference in the frequency of these engine "stumbling" episodes. However, it's been 8k miles since they were last cleaned, so they are due for a cleaning soon and will take care of that this weekend.


It is noteworthy that I have not had any engine "stumbles" since I replaced the plugs pictured above (however, I've only driven ~130 miles with the new plugs thus far).

Thank you for the input and suggestions, it's greatly appreciated.

 

Note: On an S2 a 20 brake pedal stomp is not the correct profile reset procedure. For an S2 you will need to disconnect the neg-battery terminal and depress the brake pedal shortly thereafter.