I bought locally a gently use Pure Innovations 5/16 spacer and installed it myself. I followed the motordyne guide even if the spacer comes from a different factory, and progressively tightened the bolts to 100 in/lbs.
Now I get a pending code P1283 which should mean I'm running lean.
Suspecting an intake leak? Idle sounds fine and never stumbles or hesitates.

I have a VQ35DE from 04 not a high rev. Also I kept the original gasket on the lower plenum.
So it's: lower plenum > oem gasket > spacer > spacer gasket > upper plenum.

Also wanna add that AT IDLE
short fuel trim 1 : between 3.9 and 5
long fuel trim1 : 4%
short fuel trim 2: between 9 - 13
long fuel trim 2: 0.7%

tested plenum gasket and bolts with starter fluid trick and idle didn't change

 

Breathing mods will have you running lean. Is there anything else done to the car?

 

Found this: https://my350z.com/forum/engine-and-...ode-p1283.html
and "take out the ECU 15amp fuse in the battery compartment simultaneously with the 10 amp ECU fuse in the driver side fuse box for 10 minutes.

Now short fuel trim 1 & 2 are very similar to each other and range from 3 to 8% at idle. If they stay on those values the code shouldn't show up anymore.

Another interesting thread on the P1283: https://my350z.com/forum/maintenance...s-p1283-2.html

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No. I've only done this 5/16 spacer mod.

 

Well after about 3000 miles the CEL showed up again, as pending P1283 (supposedly Air fuel ratio (A/F) sensor 1 (Bank 2) lean shift). Now the gas milage is sh¡t but performance wise it seems the same. Also on cold start, while idling it smells hella rich.
Still haven't figured out the issue but here's the screenshots I took at idle with my cheapo obd2 maybe someone can shed some light.






In regards of the value Bank1 Sensor2 at 99.2% I found lurking on other forums: "Bank 1 sensor 2 is not valid data. The only sensor you care about is bank 1 sensor 1. You can stop the goose hunt as it relates to the bank 1 sensor 2."