We bought our 2011 Outback 2.5i in July 2016. It was high mileage (162k), but we snagged it for cheap. The car was in great shape, but had a bad viscous coupler; I replaced that, and all has been bueno...for the most part.
We drove the heck out of the car these past 14 months, and now the odometer reads 187k. I did all of my fluid changes ahead of schedule, and the car only burns an insignificant amount of oil (less than 1/2qt) in the approx 5,000miles between oil swaps.
Anyways, ever since we've owned the car, it's irregularly thrown P0304 misfire codes (perhaps once every 2-3 months), and it's typically when the car is under load and being lugged (manual transmission), or coasting down hill after a mountain pass. Also, very rarely, it'll throw a P0420 Catalytic converter code. The car also began to idle slightly rough on cold startup, but runs smoothly once warm or if you "blip" the throttle on startup, thereby reducing RPM (and leaning out fuel/air mixture??). A month ago, I replaced all of the spark plugs. I found oil on TOP of plugs 1 and 3, but the tips were all on the whiter side of tan.
All of these symptoms were leading me down a path that made me believe I had a bad O2 sensor (or both sensors), or a bad catalytic converter, which was causing such intermittent codes.
The Question: Finally, to my reason for posting. I recently broke my leg, so I'm not doing any car maintenance for a while. I wanted to take care of the car's timing belt (and all that goes with it), since I don't know when was the last time it was changed. I took the car to a reputable Subaru shop, who many people with high horsepower STI's trust....seems like the right guys to work on our Outback's engine. I asked them to diagnose the rough idle and codes to see if they could make any headway on what was the cause. They couldn't replicate the issue (like I said, the car runs great), and suggested a compression/leak down test to verify the engine's health. The results below:
Compression PSI: 1 - 195, 2 - 215, 3 - 195, 4 - 225
Leak Down Percentages: 1 - 35, 2 - 40, 3 - 33, 4 - 23
These numbers are crazy. They suggested a new top end, and I suggested a completely new short block and top end....
The more I think about it though, the more I begin to question the test. The car runs smoothly and still gets nearly 28MPG average. Wouldn't numbers like that mean it would barely run? Is there a decent likelihood they botched the test?
Your help is greatly appreciated! I'd rather not drop $6500 on a new motor if I don't need one. But I also don't want to put $1000 towards a timing belt job on a motor that's about to grenade itself.