I’m guessing here but it’s most likely due to how the 02 sensors were reinstalled. They may have reversed the 2 on 1 side or both sides. I watched this video below and installed my full dundon system myself on a creeper over 3 days. 2.5 hours per day so that I wouldn’t overthink or over work myself. Came out perfect.

I really don’t trust anyone working on my cars nowadays. Even dealer. Good luck.

 

Reversed O2 sensors will throw cat inefficiency codes right away (P0420 and P0430). I dont think this is that.

 

I have a CEL and both of those codes.

 

Ok then if it was me, I would try to reverse the O2 sensors and see what happens before reverting everything back to stock.

 

I also have a 992 touring 6MT, mine is stock with just over 300 miles and I have to say it sounds like auto stop/start, if you disable this does the problem go away... sorry if you already said you tried this, just wanted to share that everything you describe is exactly what I experience in my car except my idle is smooth as it is bone stock.

 

I would remove one after cat o2 sensor, see if there is a part number on it and ask your dealer if that is the correct part for after cat O2. That way you will know which bank is correct and which one isn’t.

 

Definitely not start/stop. I thought the same thing the first time it happened. I have it turned off in Sport mode and the. Nature of the problem is that the idle is fine for a bit, gets progressively less smooth and then stalls out. Restart requires ignition being turned off and back on again.

 

Wasn’t there someone else reporting an issue and discovered it was an issue with the O2 sensor a gf how the mechanic didn’t install it properly when changing the exhaust. I seem to remember something like that.

 

Update: Turns out it was a bad O2 sensor. Car is running perfectly at this point. This is with the aftermarket headers, cats and exhaust.

 

How you liking the car? Thoughts vs. TTS? Do you have a Tecnica allocation?

 

I really like it. The TTS is obviously much faster. It's not a GT car, but the car actually handles fairly well considering the extra weight and AWD. It's a great car for daily use and longer trips. The GT3 is just a far more engaging car to drive and feels so much more mechanical. There's always been this idea that GT3 and TTS owners are two different breeds. It used to be pretty common that if someone asked for a comparison in either forum they would be met with the response of, "If you have to ask, xxx is not for you." I don't think that's necessarily the case with the current generation of cars. You just have to ask yourself which you would be happier with more often than not. Both cars in the stable would be pretty epic.

As far as the Tecnica goes, I have the order in place but still no allocation. My dealer says that production will run through 2024. Tecnicas are sold out, but apparently those with orders in place will be getting a car, depending on the dealer. Just have to wait it out - and then figure out what I'm going to do as I can't keep both the GT3 and the Tecnica together.