Recently had a disturbing loss of power on my 2007 Legacy with 211k while driving on the highway about 70mph.  The power loss was accompanied by a poof of white smoke and haven't gotten power back yet. Now drives fine on flat plane but can hardly make it up hills.  From what I've read so far it seems to be an omissions issue and not the head gasket which is a relief.  Hoping for the right answer here.  Heading in today to change valve cover gasket and front oxygen sensor, which had already been scheduled.  No Subaru dealership nearby so my mechanic might need some input.

No CEL?

 

I'm just guessing, but maybe the cat bit the dust. If it has dislodged innards it could be partially blocking the exhaust.

Yes you are correct, thank you for your advice.  Turns out there are two cats on it.  Rather expensive to replace I'm sorry to learn.  Seems I waited too long to replace my faulty upstream oxygen sensor.  

The ex valve guides have droped have had many with this problem pull header look up port check the heights of valve guides the ones closest to the port are the worst. The one I just did yesterday had 4 out of 8 ex guides droped and they had broken bottoms of guides and would not let valves close. Misfireing poping rough idle lack of power. the local machine shop knurled and pressed in new guides and engine was fixed and ran 100% better

could you have slipped cam timing? One or 2 teeth might just drop power a little.

 

at 211K miles, you're due for the second TB change unless it was just done.

Well it turned out definitively to be the cat.  Took a look inside and the thing was coming apart and blocked. Thanks for the other expert advise.  That guide valve issue sounds bad and I hope it doesn't develop.  And Lucky Texan you;re right I just put a new TB on it a few months ago; wish I had done the oxygen sensor then too.  Its a great model and I hope it keeps keeping on.  Do you guys think the engine can top 300k?  

I think the highest one I have seen is 425000kms and still going Did you look at the guides when you took header off ?

I didn't know about that valve issue when my mechanic had the cover off so I can't report on that.  But evidently that wasn't the issue, but good to know.  I do have a new problem to ask you experts about.  I live in a small town without a Subaru authority so your input would be especially helpful.  The problem is my engine is now having a really low idle.  In the past each time the battery was disconnected it took the car about 6 to 10 starts and then it would get itself back to perfect idle.  Its been almost a week now and its not resumed course.  If you have any advice I can pass on to my mechanic I'd appreciate it.  Can the fuel flow be manually adjusted in the engine or is it all computer driven?  Incidentally I no longer have a check engine light on.

Takes about a 50 km drive to relearn the idle settings on drive by wire