I'm looking to see if anyone can identify this possible missing vacuum hose on the intake manifold. I just noticed it today when i was changing my spark plugs. The engine bogs down when i cover it with my finger, there is vacuum present at this connector. It is the silver vacuum port dead center of the photo. Also there is a vacuum hose directly below this port connected to a vacuum line with a T connector and inline filter. The car is a 99 outback, but the engine is from a 96 legacy. Thanks for any help.

Edited September 19, 201114 yr by rendoll911

It goes to one of three things. The Map sensor on the passenger strut tower. The fuel pressure regulator. Or the Evap purge control solenoid under the intake runners on that same side of the engine.

 

If your hood is the original hood for the car it should have a diagram of all the vacuum lines on the engine.

The problem is my hood shows the diagram for a 99 engine and this is a 96. The diagram on my hood only shows one hose coming from this area.

the 99 has only one line going to the strut tower and the 2 devices are in line, one connects to the other. the 96 has 2 lines going to the strut tower, one to each device.

Ok, then just plug it and it should be fine. You want what's on the engine to match the original routing as closely as possible. If there was only one hose there before, and that hose is hooked up, then it's just an extra port that can be plugged off no harm done.

Ok, then just plug it and it should be fine. You want what's on the engine to match the original routing as closely as possible. If there was only one hose there before, and that hose is hooked up, then it's just an extra port that can be plugged off no harm done.

 

I was thinking i'd do that, but when i block that port it bogs the engine down like its going to stall, then the idle speeds up to save it

then get another ''T'' and a section of vac line and tie it into the one going to the strut tower.

 

as a matter of fact, double check that the all of the line on the existing ''T'' are connected to something. the third leg may be loose.

I have that too. On my 98GT the original 2.5 only had one nipple there, and the engine I swapped in had two. I just covered it off. No CEL codes for evap or any crap like that.

then get another ''T'' and a section of vac line and tie it into the one going to the strut tower.

 

as a matter of fact, double check that the all of the line on the existing ''T'' are connected to something. the third leg may be loose.

 

Just double checked. All the lines are connected. I'll try tieing it into the other strut tower since it seems like its causing engine hesitation when i just block it off.

Just double checked. All the lines are connected. I'll try tieing it into the other strut tower since it seems like its causing engine hesitation when i just block it off.

 

Since the engine is accounting for the vacuum leak, when you block it off it starts running a bit rich. Block it off right there on the intake and it'll be fine.

With a leak like that, if you drive through something really dusty you could get a lot of dust in the motor.

I was thinking i'd do that, but when i block that port it bogs the engine down like its going to stall, then the idle speeds up to save it

 

The ECU has adjusted idle speed and fuel mixture to account for more air entering the engine through that nipple.

Plug it off and disconnect the battery for a few minutes to clear the ECU then reconnect and let it re-learn the fuel settings. It will probably run a little strange for a few minutes while it figures out the best mixture and adjusts idle speed.

I know this is old, but I just wanted to add that on my 99 Forester, I have a hose running from here to my cruise control.  For some reason, when I replaced my head gasket this hose really wanted to go the wrong way, so that was a bit of a decoy.  Someone over at SubaruForester.org was kind enough to set me straight.