Revving at idle?
 

When at idle intermittently revs from about .5 - 1k..

any clues what this could be?

Car is a 2016 , about 40K, delicious stg 2 tune (although back to stock header).

Do you have the ac on?

I'll look to see if I have the ac on Mr. ac.. That'll do it?

Idle will change as the compressor turns on and off.

Lol oddly my rpm drops at idle with the ac on. It goes from 900 to 500 then 2 seconds later it up to 900 -ish. But mines a 2013 and it's an known issue from Subaru, not really a problem but if I recall there is a tbs or whatever it's called from the dealer.

As to your problem it's gotta be the tune. That's something I don't know jack about. Hopefully others would chime in on that.

Had this same issue on my car (no ac. Almost never use it) and it went away after flashing my ECU to stage 1 with the OFT. it's smoother than ever now.

The AC doesn't even need to be on. If you have the HVAC dial set to the windshield (or a combo including it) and the fan on the compressor will still kick in even on a heat setting. The compressor kicks on to dry the air for more effective clearing of the windshield.
It is not at all uncommon with low displacement engines it is just a bit more noticeable with these.

Also worth noting that running the front defogger kicks on/off your AC compressor, which will cause a small RPM surge.

Edit: Tcoat beat me to it!

Do you know if there was an aftermarket header with the Sgt 2 tune? If it was tunes with that and you put the stock header back in that cause weird issues in AFR and causing your idle issues plus others possibly

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