Hi, Does anyone know what this little hose is and what it does? Can it be left off, or does it do something vital. It's very narrow, black and stiff. It's about 3mm in diameter. It runs next to a very similar white one, from the air box to somewhere. It is 15 in. long and has a larger right angle part (that broke) of hard plastic. I repaired it once before but bumped into it again today and it popped off. Any help would be great. THanks! [non-turbo]
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'97 855na, Mobil 1, K&N, various IPD's and eBay's

Found something here:
http://volvoforums.com/forum/volvo-850-16/vacuum-line-air-box-14968/
but still curious
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'97 855na, Mobil 1, K&N, various IPD's and eBay's

-got a resolution. -for NA models
http://www.matthewsvolvosite.com/forums/viewtopic.php?f=5&t=23617 this one shows the bottom of the airbox with the mystery hose. The answer to the hose is it connects from the top to the bottom of the airbox and somehow controls a cold start flapper inside the angled section. I was able to open the angled section and remove the flapper (the hose is now gone too)and seal off the warm air intake section. The whole story is here with no one saying 'I had trouble with the mod and had to switch back' http://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=8830 Also my '97 configuration is different from the ones shown in the thread, but no troubles.
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'97 855na, Mobil 1, K&N, various IPD's and eBay's

I found it yesterday afternoon on my 1996, too late to respond to you. I intend to do the same to my car and get a couple of nipple covers to block the small vacuum holes.

I also need to investigate using a bottom section of the air cleaner from a turbo model. I believe all I need is the intake air hose from the radiator, easily obtainable at the pick&pull.

It really made a difference for me -and much more than the 'just washed the car' difference. You need to do it asap. The pick & pull will be cleaner, but gutting the existing will be easy and free. Let us know what happens.
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'97 855na, Mobil 1, K&N, various IPD's and eBay's