help with vacuum tree with pic

[ctk]

1994 explorer 4.0 automatic 4x4

The other day I went to start my explorer and it stalled after a few seconds. I was able to start it back up but it was idleing rough. I was looing under the hood and I could hear a loud hiss. I found an empty fitting on a vacuum tree near the rear of the intake manifold. I plugged it with my finger and the idle smoothed out. So I capped the nipple off and let it idle for a bit. Idled good but a little high. I can still hear a small hiss coming from this area. Im guessing the open nipple must have a hose that goes to something. Im not familar with new motors( my newest car untill this explorer is a 1978)
The nipple im talking about is the red capped one in the pic. Any help as to what this goes to or if its just an empty fitting from the factory. Big hose in pic is for the brake booster.

http://i1115.photobucket.com/albums/k543/redriderctk/swampertires003.jpg

 

[Maniak]

It doesn't actually mater which "port" on the octopus the lines are on so over the years you will end up with different ones capped.

In general, you have one that goes to the Fuel pressure regulator, EGR, vacuum canister, cruise control and the automatic trans if you have one. The brake booster is also on that octoopus. Any other fittings should be capped off. Over time, those caps can get dry/cracked and leak or just blow off.

Also, if you have an automatic trans with a bad vacuum modulator you will suck ATF up the vacuum line which then makes the caps and lines soft and they will blow off.

If the Fuel Pressure regulator diaphram ruptures you will get bad gas mileage AND fuel will come up the lines and contaminate the caps/lines and make them want to come off too.

~Mark

 

[ctk]

thanks
My problem has been fixed. I found another line at this tree was cracked.
All systems funtioning properly.