I ran into this same problem with my "other" VQ35DE in my altima. I installed headers and they ran extremely lean. A AFC or even just a fuel pressure regulator will work just fine. But the AFC gives you the benefit of being able to use it on the next mods too.

Yes the tailpipe method is a poor method for measuring AFR, but it does work. Before you spend the money on an AFC, have the car redynoed to see if maybe it just is either the ECU settling into the enhanced airflow or if it was the sniffer wideband sensor at fault. Then make your decision. Until then listen closely for pinging and detonation and make absolutely sure you are running the best fuel available.

Better Life thru Chemistry
Black on Black 03.5 Sedan 6MT - Goodyear F1 GS-D3's 225/55/17, Custom Intake Tube, HyperGround Kit, Magnaflow resonator.

 

By the way I called this cool young service guy at my local dealer and he said that the infiniti reps. confirmed with him that by unpluging the battery over night causes the computer to reset just as if they were to do it there for me. He just said when I plug it back in drive the car hard for the first couple of minutes, I am going to try this tonight, and then head back to the dyno this weekend. If no luck I see an Apex AFC in my future.

Caribbean Blue 2004 G35c w/Navi
19x8.5 Racing Hart CR's 245/35/19 on Toyo T1-S
19x10 Racing Hart CR's 275/35/19 on Toyo T1-S
TEIN Basic coilovers
Nismo Intake
DC Sport Headers
Greddy Exhaust