Subaru code P0400The first thing that comes up is a blockage in the vacuum...

[patriots27]

...system, can't find it. the second t? The first thing that comes up is a blockage in the vacuum system, can't find it. the second thing is the EGR valve, but that also seems to be working. The motor seems to run better when it is cold. The car is a '96 Legaccy Outback with a 2.5 . Is there a egr soliniod & if so does it come with the valve. Will the combination of AWD tires on one axle and regular passenger tires make any difference, they have very simular tread patterns.Have had 4 wheel drve before and was alwys told tread pattern should always match.

 

[EricF]

on subaru's the tires MUST always match. the transfer case system can not handle different tires, it adds stress to the system. the system also does not like uneven tire wear, like the front tires having less tread than the rears. that's stress too. the system is very good, but this quirk to me makes it a mess.
constant tire rotations help a lot.

back to your problem.. the vacuum system is more than the EGR valve, there's a pressure sensor, vacuum sensor and hoses.
you have to start breaking everything down. clean the egr valve, and the hoses. you probably just have a high carbon buildup and it's blocking flow.
take the egr valve off, clean it, and make sure it holds vacuum.
spray lots of carb spray into the base where the valve bolts down on.

you might want to consider decarbonizing your engine. Use Seafoam for that, it works very well. But goto Youtube and type in Seafoam for a video of what it does. it looks very bad, but in 30 minutes, your engine will breath much easier!