Last April, Nismo3112, BlackBIRDVQ, and I swapped a 3.5L out of an 02 Altima into my 4th gen. For the first few months, the car started like it came with the setup from the factory...turn the key, it fires up. However, as the summer progressed, it got harder and harder to start requiring me to feather the throttle as I started the car. After storing the car for the winter, I tried to start it but all it would do is crank and crank. Flooring the gas would allow it to fire up eventually but then I would have to feather the gas some more to keep it alive for the first ten seconds or so. I need some help figuring out what's going on.

My setup:

02 VQ35
Pathfinder throttle body (properly calibrated TPS)
SSIM
Walbro 255lph fuel pump
Nismo FPR (gauge is showing 38psi when idling)
Returnless fuel setup
VQ35 injectors
IACV relocated and hooked up using a Stephen Max adapter and a new inlet was drilled and tapped right by the brake booster barb on the IM; vaccum hose between the IACV and the barb is about 2"

 

Forgot to mention, I have one 1105 code for the MAP/Baro solenoid however that shouldn't affect start up, should it?

 

Well, the 1105 code will not affect start-up at all, so ignore that for now.

I would look for a vacuum leak, perhaps even a large one. With all the intake mods necessary to swap in the 3.5, including the IACV set-up, there is a lot of potential for creating a leak which would cause this condition.

I know because I had one shortly after my swap. The large hose leading to my IACV was actually collapsing under the negative pressure and sucking air at the connection I had made.