How much time do you have?

Ok, this is my educated guess so anyone can reply if you think I am off on anything. A lot is based off my knowledge from my E36 which has a carbon canister in the similar location as the X5.

Anyways... a fuel system by law must be a closed system meaning no gas or vapors can be released into the air. Gas sitting in your tank, especially a full tank will release vapors which must be collected by the vehicle, usually in a carbon canister. When your car sits for any amount of time this canister will fill with gas/gas vapors and will be vacuumed out when you start the engine. This vacuum empties the canister and pulls the vapors into the intake manifold where it is burned off by the engine. This is all done in the name of emissions control.

This is why I believe only the 4.4 from California have this tube to the airbox and there is only a vacuum in this hose at engine startup.

my 4.6is has this same tube. not-2-mention an additional
tube that no other model X5 has. check out my thread
here.

ah ok, makes sense. cuz this morning i noticed it literally is a sucking vacuum effect that suddenly shuts off once the temp needle exits the blue.

good thread. The same issue that i came across last weekend installing my AFE. Thanks guys especially OP!

That small filter came with my AFE (I purchased it from Bavarian Autosport)

So is this only on vehicles with California Emission Control device? My 300ZX also has a carbon canister, which i will eventually remove to shed some pounds.

I don't recall seeing this tube on my x, but now I will check again.

how is the performance

on mine, this is what i noticed:
quicker response, when i floor it the RPM doesnt go above 4000 and shifts right away, and of course, a lovely sound. :thumbup: driving is more fun now highwaay and city, it seems to take you up to speed in no time. But could be me, or its all in the mind, but on a 4.4L engine, i would recommend this!