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Old 08-24-2009, 09:54 PM   #1
Darren_2.5RS
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Default Misfire or sluggish? No CEL? Intermittent!!

I am looking for some help with my non-modded 02 Impreza RS.

A few weeks ago upon a cold start my car started running rough, typical feeling of a misfire. I only got a minute or two from the house and it threw a code P0303 (#3 misfire). I brought the car back home and let it sit for a while and tried it again and it ran fine so I cleared the code and was ok for a few days.

Eventually it happened again but this time threw no code. Again, I used it for about a week and a half until this morning when it got worse.

It cold started ok but after a mile of driving it started the same misfire type running, hesitation poor idle and eventually got worse to where it seemed like it was running on half the cylinders or less. I was able to turn around and barely made it home. The odd thing is that at one point I shut the car down and restarted it and it ran fine for a few seconds (maybe 30-45) but then started running rough again. The car had new plugs and wires about a year to 2 years ago so I thought perhaps it was a coil pack.

I tried that later in the day and the car ran ok for a little while until it eventually started running terrible again after I got on it (70 mph @ about 4k) again it was a struggle to get home. I again shut it off and restarted it and once again it runs ok for a few seconds then it starts running rough/misfire. I was able to repeat this a few times. And all this time no CEL. But I then checked the codes again and found a P0734 (4 gear incorrect ratio). I once again cleared it, put back the old coil pack and took it for a ride 2 times and it ran well but I didn't get on it, just drove normal?

At this point I don't think plugs, wires or coil are a factor. Would be interested to hear from members with far more experienced than I.

Thanks!
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Last edited by Darren_2.5RS; 08-24-2009 at 10:35 PM.
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Old 08-25-2009, 07:07 AM   #2
Darren_2.5RS
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Anyone? Thanks.
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Old 08-25-2009, 07:51 AM   #3
Charlie-III
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How many miles on the plugs & wires (time is only part of the info)?
What plugs & wires?
Did you change gas stations recently?
Has the weather been a lot different than normal recently?
Have you done any other work on the car just before the onset of the initial issue?
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Old 08-25-2009, 08:26 AM   #4
Darren_2.5RS
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I would say perhaps 40k miles on the wires and plugs. I can't recall what the wires are and would need to check them. However, I know I went with NGK (probably V-power) plugs as they are pretty much all I use in all my cars.

As far as gas stations, I usually hit all the same ones on my route. The weather has been pretty normal around here mostly dry and sunny. But the problem has happened during a high humidity spell as well..

Around mid summer I had my transmission completely rebuild. I was wondering if this might be torque converter related but the problem still occurs in neutral and park.
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Old 08-25-2009, 10:07 AM   #5
Charlie-III
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I would pull the plugs (40K miles on them) and look them over.
1-You may have one or more that are worn (copper plugs wear faster than the "special metal" but you already know that)
2-You may have a plug well seal failing and soaking the plug & wire causing an intermittant short (AKA, misfire)
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Old 08-25-2009, 01:26 PM   #6
yarrgh
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agreed w/charlie. Look over all the connections to the plugs, and the wires very thoroughly to see if you can spot a place where it might be arcing to ground instead of the plug itself.
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Old 08-25-2009, 01:41 PM   #7
Darren_2.5RS
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Much appreciated guys. I'll look it over this evening.

Does that symptom where it runs rough but then I shut it off and restart it is ok for about 30-45 seconds make sense to anyone?

Last edited by Darren_2.5RS; 08-25-2009 at 02:24 PM.
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Old 08-25-2009, 09:23 PM   #8
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Ok, the NGKs were a bit beat up and out of gap. I also changed the fuel filter and took the car for a ride with no issues, hesitation or rough idle. So far, so good. Hopefully it lasts.
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Old 08-26-2009, 08:42 AM   #9
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Hmmm. The car still seems to be having problems.
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Old 08-26-2009, 01:41 PM   #10
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Things I learned to check were cam/crank sensors. They wont always throw cel's when they start going. You already checked plugs, and coil. Have you looked at your wires? They do make a difference, could be a bad batch of fuel like others thought of already. have you done a t-belt lately, maybe its jumped a tooth. just trying to brain storm causes.
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Old 08-26-2009, 02:41 PM   #11
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2 years ago I did both head gaskets, water pump and belt so I would think I am fine there...

Where are the cam/crank sensors located and how are they tested? Appreciate the reply, thanks!!
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Old 08-26-2009, 10:13 PM   #12
yarrgh
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crank sensor is located directly under the alternator. Cam sensor is on drivers side cam, under/to the side of AC compressor.
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Old 08-27-2009, 08:22 AM   #13
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Yesterday I topped off the tank and added fuel injector cleaner. I also added 1 of the ground mods and reset the ECU. I did 25 miles last night with no problems and 25 this morning without issue. See if it lasts.
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Old 08-28-2009, 11:41 AM   #14
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After about 2 days of good luck I eventually noticed more hesitation but not nearly as severe. I performed a water spray test on the plug wires and found that #3 was arcing. Note: the first code I found was a P0303.

However, I still seem to have some hesitation going on. Hopefully I am getting closer. So far I am only $28 into this problem which is nice.
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Old 08-29-2009, 09:23 AM   #15
Charlie-III
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Unless you bought an OEM set of wires, I would look them over carefully.

Bosch wires cause issues with Suby engines (just like Bosch Platinum plugs), I have no clue why but I have put them on myself and had issues that were resolved by going to NGK copper plugs and OEM wires.

There only a few parts that I insist remain OEM,
-Rad cap
-Plug wires
-Thermostat
-Rad hoses
-a few others that escape me right now.
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Old 09-01-2009, 11:05 PM   #16
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Seems like the random hesitation and rough idle only occur after it is warmed up real good.
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Old 09-02-2009, 12:14 AM   #17
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thermostat maybe. my car was having problems like that earlier in the year which was causing it to run rich as **** and it was smoking from the exhaust. is yours doing that? i changed the thermostat and all of the ominous running issues went away. heres a write up i would reccommend to any of my legacy fellos but this might help you out in terms of pointing you in the general direction as well.

http://www.lovehorsepower.com/Subaru...empSensor.html
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Old 09-02-2009, 12:26 PM   #18
Darren_2.5RS
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No, not running rich or smokin. If it was a thremostat I would think it would be pretty noticable. I am wondering if my front O2 sensor is goin..
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Old 09-09-2009, 01:13 PM   #19
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I am still having the same trouble with no CEL to speak of. I suspected a fuel delivery problem so I hooked up a fuel pressure gauge between the filter and the motor and am getting 44psi with the vacuum disconnected and about 36/38 with it connected. I also just found that my long term fuel trim is in the -20%s. Gonna try the 02 sensor.

Last edited by Darren_2.5RS; 09-09-2009 at 02:50 PM.
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Old 09-10-2009, 09:45 AM   #20
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Replaced the 02 sensor and drove the car on a couple trips last night about 12 miles and it ran like a top. Also, did a 26 mile stretch this morning without a single hesitation and near undetectable idle. Checked the fuel trims and they were hovering around 2-3%. I think that might have got it. Fingers crossed.
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Old 09-10-2009, 04:26 PM   #21
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How's your oil consumption? I was having trouble in my 05 RS for a while. It turned out to be my valver cover gaskets leaking and interupting the spark. I would check your spark plug wires/covers for oil residue. It seems to a be a fairly common issue after about 70k

Mike
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Old 09-14-2009, 07:43 PM   #22
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I have the same symptoms and no CEL. Did the new front O2 sensor solve your problems?
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Old 09-15-2009, 11:02 AM   #23
Darren_2.5RS
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Yes, the car runs like new now.
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Old 09-15-2009, 12:09 PM   #24
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Quote:
Originally Posted by Darren_2.5RS View Post
Replaced the 02 sensor
I am having the same issues but cant pull the code yet but there is really bad missing. I still cant find the problem. Which 02 sensor did you replace? I have my 02 sensor spaced and I am wondering if that may be the cause.
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Old 09-16-2009, 12:43 PM   #25
Darren_2.5RS
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I changed the front one. Rear is for monitoring.
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