Posted this on my350z hoping for more traffic, got nothing. Cleric?

Every 25 seconds idle drops to almost stalling for a few seconds then comes back up. Idle has continually become choppier.
05 6mt sedan so revup. Has standard breathing mods, uprev tune. Setup has been the same for years without issue.
118000 miles so I replaced pcv valve, new ngk spark plugs, hitachi cam, crank and maf sensor now. NTK O2 sensors 4 years ago.
I reinstalled and re-torqued the MREV2 plenum and 75mm tb adapter. Capped off vacuum lines and sprayed brake cleaner looking for leaks.
No codes.
Like clockwork it ONLY dips every 25 seconds never misses a beat. Warm or cold.

 

Have you checked the 3 PCV hoses?

I would smoke test the intake.

The 25 second thing is odd though, real-time scan your short term fuel trim to see if it's pulling more and more fuel then resetting after the near stall.

Also could be EVAP related, Turn the engine off then quickly head back to the engine bay, side of the car, under the trunk and listen for any hissing noise.

Also test for fuel pressure, does it only do this at idle? What about driving down the highway at higher rpm, do you still feel the stutter?

 

Fuel trim is solid 25% idling then drops straight to 0% sputtering. And now also I've monitored it a few times at cold start up and it alternates dropping just bank 1 or bank 2. Then synchronizes both banks together. Still 25 second intervals like clockwork.
Only happens at idle, no other change off of idle.
I "tested" hoses by capping everything off at the plenum. Still fizzles out every 25.
Haven't smoke tested, checked pressure or listened for EVAP yet but EVAP hiss i likely would have noticed when parking in my garage...

 

What happens if you hold at like 2000 rpm, does it still sputter out on interval?