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2009 Forester 2.5X Prem 5 Speed MT
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Discussion Starter · #1 ·
Hi all. I just made an account here to post about this in case it helps anyone else out in the future.

Two years ago I moved from the Midwest to the Denver area. The day after, I noticed a hesitation in takeoffs, and had to ease the clutch in a lot more than normal. I took it to a reputable local place and they claimed it was the altitude, which is something I hadn't considered at the time, and it is true that my NA engine will have less power up here.

I left it to that but over the next two years it seemed to get worse and worse, but ever so gradually. I kept going to the same shop for regular maintenance and repairs and always mentioned this but people weren't really able to pinpoint anything.

Finally about a week ago it got A LOT worse. Takeoffs were very shaky and I was throwing a P0303 cylinder 3 misfire. I took it in to the same place and they diagnosed it as a leaking spark plug O-ring that was now shorting the connection. They replaced the spark plug, seal tube, O-ring, and valve cover gasket and my car runs good as knew from back before I moved out.

I know acceleration hesitation can have a lot of sources, and I know oil around spark plugs isn't an uncommon issue, but what I definitely didn't know was how progressive that kind of issue can be without a CEL or other obvious problems. I didn't really start tracking my oil consumption till lately, and before this repair I was killing 1 QT about every 700 miles, which is even on the excessive side of the already high burn rate of these engines. I'll keep an eye on it for the next couple months and see if that's improved at all with the fix of this leak.

I hope this helps someone down the road who thinks they're crazy that their cars performance suddenly decreased without other symptoms.
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