1995 Subaru Wagon engine shake, knock

1991 SUBARU LEGACY
200,000 MILES • 4 CYL • AWD • MANUAL
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LBEAN
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I have a 1995 Subaru Legacy Wagon 2.2L AWD Auto. It is running a little bit rough:

putting sound each revolution coming from exhaust,
slight knock at higher RPMs,
small lack in power,
and the engine shakes side to side while idling.

These symptoms only happen when the engine is fully warm.
It has about 211000 miles now. When I put higher octane gas in, it is better for about 10 minutes, then reverts to the same symptoms. In the 3500 miles since I got the car I have:

replaced oil/filter twice,
replaced valve cover gaskets,
thermostat,
gave it seafoam (just before last oil change),
treated oil with that stuff for stopping smoking/blowby. It wasn't really smoking, just thought it might help.

What course of action would you recommend to fix this? Everything is in good condition including air filter, and recent timing belt job, and only very slight oil dampness on the valve covers. I don't know any history about the head gasket, but it is a reconstructed car within the last 3-4 years so it could have a rebuilt engine, who knows... None of the things I've done have made any difference in the shaking, knocking, or putting, although I seemed to have a slight bit more power after seafoam. I was losing about a quart of oil/1000mi, don't know yet if that part is better. Hoping to get a bit better mileage and a lot more miles out of the car, it's not too bad at 24-26 on highway but I know it could be better.

May 13, 2011 at 7:53 PM
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FIXITMR
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first thing i would do is a compression test.
May 13, 2011 at 9:34 PM
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FIXITMR
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so it's a 91 with a 95 engine or the other way round?
May 13, 2011 at 9:48 PM
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LBEAN
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I don't know why it says 1991, that's my other car... I thought I selected all the right info, I'll try adding the car later... Its the 95 2.2 at awd. Forgot to say I also did spark plugs. I'll look into compression. Thanks
May 14, 2011 at 4:00 AM
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FIXITMR
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when did this start? any relation to timing belt job? was that just a preventative maintenance thing?
May 14, 2011 at 3:36 PM
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LBEAN
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I don't know why the timing belt was done, it may have been preventative... The previous owner did do a lot of preventative. It has progressed slowly since about a week after I bought the car.
May 14, 2011 at 7:06 PM
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LBEAN
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Specifically, i bought the car with 207,000mi, and the shake and putt grew from
208 to 210 and stopped there. I'm at over 211 now.
May 14, 2011 at 7:09 PM
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FIXITMR
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any luck yet?
May 26, 2011 at 11:39 PM
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LBEAN
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Compression tested 140, 160, 150, 160. Talked to a Subaru guy who said not to worry about that just keep checking oil.
The putt coming from exhaust is mostly better now, maybe the ring sealer I put in the oil?
There is still a knock/tap, sometimes varies. Has to do with fuel grade I think, but can't figure out what works best, results are inconsistent.
May 27, 2011 at 5:45 PM
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FIXITMR
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i think the engine needs rebuilding. tired out.
May 27, 2011 at 6:33 PM
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LBEAN
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Ok well I'm in UT right now, hopin to make it home to AK then I can rebuild. I'll be in touch then haha. Thanks for the help
May 29, 2011 at 4:40 PM
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SIXPACK SUBARU
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Could be just lifter noise and associated lack of performance as a result. Thicker oil, (anti-smoke compound), would point towards a possible lack in oil pressure due to loose oil-pump backing plate screws, (very common for this model). Is it worse when the engine is cold?
Jun 20, 2011 at 10:47 AM