What does tube on air intake tube do

[Journeycastro12]

Can someone explain what the tube that connects to the air intake tube after the maf sensor does, I always thought that this let fresh air into the crank case on the passenger side, and then the driver side had the pcv valve that allowed the positive pressure to be vented along with dirty air back into the engine to be reburnt, but Ive noticed I’ve been getting oil in the passenger side tube, and also a bit of oil in the vaccum tubes. Can someone explain how all the vacuum, pcv system, and passenger side tube systems all work? 08 ly7

 

[Fu Manchu]

Improves throttle response.