Failed smog test for high nox

Wife and kids were away tonight so I pulled the plugs tonight to see how they looked. These plugs were installed about a year ago and probably have less than 2000 miles on them.

They look fine to my untrained eye with the exception of plug#5 which had a carbon like buildup. I also verified all plugs were gapped at .035.

What should I make of plug#5?

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Could that just be oily goop you caught on the plug as it came out?

The thought did cross my mind. I tried to blow out each plug hole as I went but I think I forgot to on 5 and 6. It was also at an awkward angle with the heater hoses in the way which may have caused me to drag it through some dirt on the way out.
 
Alright, couple updates, as I've shelled out the big bucks. 💸💸💸

First, I did a diy smoke test and still couldn't identify a vacuum leak, so the high idle remains unsolved. My next thought is to pull and closely inspect the IAC.

I also bit the bullet and had a new cat, muffler and tailpipe installed today. While not cheap I'm very happy with the new exhaust. Catco cat and new Magna Flow muffler installed by a local shop here in OC. They do great work, plus the owner has an LJ http://ocmufflerman.com/.

Here's a shot of my cat, it's a high flow version apparently!

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I also found a Mopar o2 for my TJ on rock auto and bought that too as a possible backup plan if I fail the test again.

My preference is to test the Jeep now with the new exhaust and see if it passes without installing the new o2 sensor. Then I could just hold onto the Mopar as a spare? Or should I just install the new one?

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Decided to just go ahead and pull the o2 sensor today and I think I'm glad I did. The original appears to be a Mopar as well. It could've been me but after taking a test drive it felt like it was a bit more responsive?

Plan to retake the smog test this week sometime, 🤞.

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