Well I just have to know, and I cant quite figure out how to come up with the right words to search this thing out on my own. All of you 3.4 owners out there, does anyone know what this is and why it is there? It definitely lets in a good amount of air into the plenum, and plugging it has a noticable effect on the engine.

I am talking about the dead end tube with the little nozzle on it floating there:

 

EDIT: My mistake Habanero is spot on, I should have opened the hood and looked, leaving it open would allow unmetered air in the system making you run lean and maybe suck in debris. And that would explain why 2wd intake plenums are without that port on them.

 

On our 4Runners the 99 goes to a check valve and on down to where the 4x system vacuum lines are, the 96 uses it for the ps pump.

 

Thanks for the replies, so the best thing to do would be to cap it? This engine came out of a 99 4runner 4x4 manual.

 

Seems reasonable to me. My 99 is 4x4 manual too.

 

Well I capped it off, and seems to run better, thanks for the help guys!