Here's the story:
I bought a 1999 Legacy Brighton 5spd 2.2 in September of 2010. I made the purchase (after years of making fun of Subarus) for all that I had come to learn about them: reliability, safety, and anywhere AWD. I love the car and have put 15k miles on it.
There's only one problem - it goes through times where it stumbles/hesitates when shifting and when I release/depress the accelerator at regular driving speeds.
This stumbling is many times pronounced enough to move your head in a whip-lash motion - you most always feel it in the seat of the pants. I say that this is a "phantom" problem because I've tried the following remedies which SEEM to work but in several hundred miles (or less) the problem is back:
1. Replaced valve cover gaskets (they were leaking into the plug wells...thought this was messing with the firing of the plugs.
2. Replaced the coil/plugs/wires (code scanner said there was a misfire on one of the cylinders.) This seemed to fix it...for a little while.
3. Replaced fuel/air filters (just in case).
4. Replaced fuel filler neck. Was getting PO440 and PO453 (Evap) codes. The filler neck was quite rusty and began to actually leak. Car ran good but soon was stumbling again.
5. Mechanic checked for vacuum leaks. None were found.
6. Unplugged the knock sensor to see if the stumble went away. Thought that it was possibly too sensitive and was mis-communicating with the ECU. Stumble was muted but very much present.
7. Engine was surging and began to run very roughly plus we had a TPS code. Replaced the TPS and it ran great for about 400 miles. Thought that
the problem had been found for sure. Tonight it randomly began stumbling again.
8. There's one ongoing issue: The PO453 and PO440 codes are still there. (Check engine light comes on and off seemingly at random.) On top of, and possibly related to this issue is the fact that it will sometimes not allow me to put fuel in the tank. Pressure builds up and it will "spit" the fuel back out. The pressure is great enough that I really have to leave the cap off for a while and then go get gas.
Any ideas? I love Subaru's but this phantom problem is driving me crazy!
