Ok, so its my Cosworth plenum that's the problem. It is leaking from the driver's side end cap. This is the same place it was leaking when it was intially installed, and was told by the vendor to reassemble and reseal the cap. This worked for a few months, But, unfortunately the issue is back. I hope the vendor/Cosworth USA can remedy this for me, b/c it is leaking badly and is the cause for my code and idle surge.

 

Did you change your AFsensor? Did it help? I am throwing code P1281 (2005 Infiniti g35 coupe)