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My car normally rumbles all the time, like a fast swaying feeling. It's not a
noise, it's what I feel when I'm sitting inside. It is fine when I drive. It's
usually fine when I stop. It normally idles at about 800 - 900 rpm's, sometimes
500 rpm's.


Recently it's been doing it worse, but chooses when to. Today it was fine. It seems like letting it sit
without driving makes it occur, say 1-2 days. It lasted for at least half of my drive if not more. I went 

to O'Reilley's and the guy there was stumped more than me.


It almost felt like it was misfiring a few days ago, like one of the cylinders wasn't turning fully and
that the ratio was off. It scared me when the rpm's went all the way down to the
first white line, very low, and it was swaying a lot more than I'm used to. It got worse if I accelerated in neutral; it would come down and low-rev shake more. It made me feel like it had 6 months or so until that shaking turns into an engine that just stops running out of no where.



Ideas: Throttle wire tension not to spec, Spark plugs, vacuum leak, EGR, timing. 

Note: MPG Perfect

I checked the MPG twice in a row. It's still 27 mpg (Perfect, to spec). In fact it's 27.09 MPG
going 80 MPH - 90 MPH, and 27.11 MPG going 75 MPH.
I use 89 sometimes, but mostly 91. (92 requirement). I never use 87 and never will.

Note: No Check Engine Light

Any other 6 cylinder subaru owners with similar problems?

2002 Subaru Outback H6 3.0 VDC Sedan - Engine: EZ30D  :)


If you can give me some help in narrowing down the issue I would appreciate it greatly.


Thank you!

Edited by Subaru02H6
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Not sure why others haven't jumped in....


Since the MPG seem OK, I'm not as confident in my suggestions...and i'm not that familiar w/the H6- but:

- Tune ups? wires and plugs? EDIT: this uses coil packs on the plugs..they could still be the issue, but not sure how to 'check 'em'.

- MAF sensor need cleaned (carefully! read up)

- Vac line issues? Car is 12 years old so hoses get brittle

 - try another fuel station




Edited by wtdash
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Yeah Subaru Nut, I don't know why others haven't jumped in either. I will say that since I noticed a less excessive rumbling start a year ago that I might just do all 6 plugs myself, well I went under and found that these plugs have only about 1" of clearance for a driver to get in there and pull them out. You almost have to hoist the engine out to get to them. It's a tough work area, but yes plugs have been on my mind for quite some time. It's $280 - $350 for that full job here in Alameda, CA including the plugs.


I asked for an engine diagram for the EZ30D yesterday, we'll see if anyone supplied it here in a second. That would help me a lot in finding where the vacuume hose is.


I will say that I do have another issue that I won't get into too much because it's exhausting writing a 2 page letter about it 30 times over but it may be related. Long story short the AC stops running cold. To make it work I turn the ac off, turn car off, turn car on, turn ac on. Clutch engages. Over 80 MPH with AC on makes car overheat. Turn off ac when that happens and she goes back down to norm temps. As far as the problem solver goes I've come to the conclusion many times over and it's the low pressure cycling switch above the dryer, passenger side firewall top. It's a real hard part to find locally, even online.

Don't even ask.



Edited by Subaru02H6
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That's probably your issue.The AC cycling.


And I'd bet it's just the O-rings where the metal lines connect to the compressor - unless it's gotten 'fried' due to overuse. Read up on here or over on Subaruoutback.org for info on the o-rings. Easy enough to do yourself, but you'd need to 'recapture' the freon to be legal.


And 'subaru nut' is my 'rank' due to # of posts. My user name is 'wtdash', not that it matters, but just for future reference. :-)




Edited by wtdash
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There are lots of reasons you can have these symptoms with an H6 model car.  To start you could have a slight leak of oil between the coil pack and the valve cover spark plug gasket seal.  Next up would be an unseated intake air tube or an idle air control valve acting up.


As for A/C symptoms make sure both fans operate when the a/c is on and that no relays are clicking.  You could be over or under filled on freon as well.  The switches and other Ac parts on this car don't often fail.  The fans are pretty common to act up and of course as I mentioned freon charge is very common especially in this day in age where we have DIY kits that do a pretty horrible job and I wish they would get rid of them completely and leave it to the professionals.  No DIY'er can put exactly 1.56 pounds of freon in a car like a true ac specialist can and when you over charge the system it does cycle on/off as a pressure switch reacts.

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