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I've been plagued with this problem for a while and figured I'd just post up a thread and see if I can get a new direction.

Generally, my car runs fine; however, sometimes it runs great. I don't know why it decides to pep up some days and even sometimes on the same day randomly during a drive. If I could get it to drive peppy all the time I would be very happy with the car. I'm hoping that in troubleshooting the below issue maybe I'll discover the reason for this behavior.

I usually only drive it around town and it gets 19-21mpg and usually smells like it is running a bit rich.

When I take it on the highway it will almost always get a misfire code for cylinder 3 and 4. The other day I got one for cat efficiency, but I do have a Stromung high flow cat on it so I just attributed it to that. I do not have an extension for the O2 sensor.

The misfire more often than not seems to occur when in the 3000 to 3500 range and I start coasting. When the misfire code is thrown the car still runs the same.

I noticed today that it will start sounding gravely at around 3000 and I can feel a distinct impact in my shifter, it gets worst at around 3200 and then smooths out entirely past 3500. At 3200 the impact seems pretty severe and I can't imagine it is going to be good to run it long term while in that range.

If I put the trans in neutral and run the engine up in RPM it isn't smooth up the entire RPM. It will get rough and gravely around 3000 and then evens out.

When at idle you can barely hear a ticking, almost sounds like fluttering, as I accelerate the noise becomes much more noticeable and is coming from the passenger side of the engine.

It seems to run better after the battery has been disconnected, and then starts getting doggy again after a few hundred miles.

It sounds like it may have an exhaust leak at the heads. The Bosal y-pipe came bent, but I was able to get it back into shape, and it seemed to install fine with Grimmspeed gaskets.

It has been run out of time a few times, so I'm not discounting something more serious. I am wanting to do a compression test and leakdown test. I am hopeful the gurus here can give me some more things to check out.

I've got new NGK iridium plugs, NGK wires, new Subaru coil, I've tried two different igniters, I've got a grounding kit installed and good clean battery contacts.

Thanks for any help.
 

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141 Posts
- Exhaust leaks - sounds like a mis-matched exhaust from the header back. Not bad, just potential for leaks....take it to a shop to weld it up.
- Miles? 105K it's due for valve adjustment (assuming it's still the stock EJ25D) - most don't bother, but I've seen (bought one) these w/BURNT exhaust valves @ less than 150K miles.
- Knock sensor> Bad KS cause 'limp mode', which would explain the change in performance. But should throw a CEL.
- Do the Leak Down and Comp tests soon.
 

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OBW H6 VDC, Tribeca, XT6
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12,390 Posts
1. swap fuel injectors and see if the cylinder misfires "moves" with the injectors. or just install two used injectors if you dont' mind spending a few bucks.

2. check valve clearance, namely the exhaust valves will be tight. that engine has shim over buckets. on shims - i just grind the side that's not touching the cams down to get the clearance i need. the crazy ordering and measuring and waiting days/weeks is nutjob.

#4 exhaust valves are most likely to be tight and burn on that engine.
 

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03 H6 OBW & 06 WRX Sportwagon
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17,816 Posts
It seems to run better after the battery has been disconnected, and then starts getting doggy again after a few hundred miles.

after a reset, the ECU uses a factory generic rom image for all learned settings. Since it seems to run better for you after a reset, likely a sensor is reading poorly and the ECU is actually learning an incorrect a:f or timing setting.

knock sensors are known to kill power and often will not throw a code. I wouldn't rule out a dirty/bad/intermittenet MAF or soem issue with the front O2 - or wiring/grounds causing issues with those sensors.
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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1,578 Posts
Check the intake tube from the MAF sensor to the resonator box for cracks, splits, and unhooked vacuum/air lines. Any leak after the MAF sensor will cause odd running behavior.

Does your coolant temp gauge also sit somewhat low in the range? Is the car hard to start when hot? cold?
 
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