Well, let me tell you...
Every time we lift our foot off the throttle is closes. We need intake manifold vacuum for the brake booster and for purging the charcoal canister. We don't have a vacuum pump like a turbo engine.

When the gas pedal's position is more than about 15%, the throttle bodies open and the VVEL system contols how much air enters the engine.

 

Thank you. Lots of people are under the mistaken impression that it's always open when the car is running, but that makes way more sense. Also explains why cleaning the TB fixes idle issues

 

You are very welcome.

When I first got my G37 I needed to understand if/when the throttle bodies close, so I logged and analyzed the intake manifold vacuum and accelerator pedal position.

The VVEL system is complicated and Nissan doesn't really explain how is operates during different engine demands. Thank goodness for OBDII data logging

 

No disconnect, removed throttle body from the intake manifold, and wiped with a shop towel. I was concerned that I would have to do an idle relearn but to my surprise, no rough idling. I can't say my future experiences will be the same but i've cleaned my throttle bodies twice with great results. I can't speak for other experiences.

 

always disconnect the battery to prevent issues