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My 02 Wagon is wigging out. It's got the cobb access port, turbo back exhaust, sti up-pipe. Bought it from a good home with all proper maintenance records. It ran great for a month after I bought it. I recently put new headlight bulbs in it. Had to disconnect the battery and the stock intake tube that opens above the radiator. Afew days after it started to misfire. Running terribly rich with misfire codes/CEL. Replaced the o2 sensor. CEL went away. Ran great on the test drive but started misfiring again on the way back to the shop. Checked records, the fuel injection hose was replaced in 07 (because of the fuel smell in the cold), as well as spark plugs and fuel filter. In 08 the MAF was cleaned. Is it due for a cleaning again already?? I'm going to check all of my ground wires and make sure the intake piece is sealed properly. Though I thought I put everything back in place after the bulb switch. I'm going to run down the checklist on this thread, but does anybody have any thoughts? I'm scared.

edit- it's not reading any codes but there's white smoke coming from engine compartment??
 

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I had a 2006 WRX TR that I was getting misfires on all four cylinders. The dealer said it was because I installed a K&N air filter and it snapped the tabs holding the air box together causing a vacuum leak. Evidently the K&N's are too tight a fit for the airbox. Just thought it's another thing you could check.
 

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I had a 2006 WRX TR that I was getting misfires on all four cylinders. The dealer said it was because I installed a K&N air filter and it snapped the tabs holding the air box together causing a vacuum leak. Evidently the K&N's are too tight a fit for the airbox. Just thought it's another thing you could check.
Considering there's no vacuum plumbing before the MAF, I don't see how that could haver caused a vacuum leak...
 

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They said it was getting to much air and the engine was over compensating causing the misfire. Sometimes I wonder if the dealers even know what their talking about. My car got totaled before I was able to resolve the problem.
 

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My 02 ran great but then my CEL came on and registered 2 misfires. It still ran just fine but I thought I would change the plugs anyway. After changing all the plugs, I took it for a test drive. As soon as I gave it full throttle, the CEL came back on and the car would start jerking as if I was repeatedly pressing and depressing the throttle. I didn't use the plugs you stated before, but could that affect the power output that much?
 

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Discussion Starter #26
Yes. If the plug gap is wrong,the coil pack not seated properly or the harness for the coil packs were switched. What plug exactly did you use?
 

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Yes. If the plug gap is wrong,the coil pack not seated properly or the harness for the coil packs were switched. What plug exactly did you use?
I used NGK plugs, but they weren't iridium. Could that cause a power loss? I just used what Canadian Tire refered me which was not a smart decision in hindsight. I'm going to run through your check list as soon as I can also.
 

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Cleaned the MAF and runs like a champ again. I'm still getting a misfire but i'm much happier now. I think I just need to get the iridium plugs and actually gap them to specs. Thanks a billion.
 

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OK my stock 04' WRX 145k miles has a P0304, and after buying the spark plugs, coil packs,cleaning MAF, and one bottle of injector cleaner still code. So a month later(today) I did a compression test......

Engine was Cold, results were: 150,150, 151, 149

Is this a good thing?? and if so what should I do next by the injectors or 02 sensor.
 

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Have 03 WRX - been dealing with P0303 & P0301 CEL

Just to reiterate. I've worked on lots of cars old and new and weird things happen. Example:

I have a 2004 wrx all stock except for the resonator box was removed. Sounds kinda nice:)

I was driving and the CEL came on. Ran the code P0301 cylinder 1 misfire. I started with the plugs and all of them were fine. I replaced them anyway because it was cheap. Then I switched the coil packs from 1 to 3. Nothing changed. Still pulled the same code. Then I checked the wires. All were fine. Then I ran a fuel injector through 2 tanks of premium gas. Finally my buddy said to pull the MAF plug while it idles and see if it improves. Guess what...

So I cleaned off the MAF and it runs fine. Just because it says P0301 doesn't necessarily mean that's the issue. That's just the first place the computer detected a problem so I had to go "further upstream."

Sometimes I wonder why I even bother lifting up the hood but there's always something new to learn.

Anyway, don't get tunnel vision like I did and if you submit something to the forum, give as much info as possible because it wasn't until I stopped thinking about the plugs (which were totally clean anyway) and considered that only the idle was rough. I never experienced a loss of power. Be thorough and provide details. Cheers

I'm sure this is a noob question to ask but what is the MAF plug? I also have an after market flywheel with a K&N air filter, Cat Back HKS exhaust. Any help is appreciated since there are so many different approaches on this forum, Thanks!
 

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On the intake there is a small electric device with a harness clipped to it. Is is about the size of a match box and located on the top of the intake after the filter section, and is black. This is the mass airflow sensor. Periodically it can accumulate dirt (especially if the filtration is sub-par -- read: aftermarket) and generate a PO171 "lean mixture O2 sensor" code or more rarely in my experience a misfire.
 

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I'm sure this is a noob question to ask but what is the MAF plug? I also have an after market flywheel with a K&N air filter, Cat Back HKS exhaust. Any help is appreciated since there are so many different approaches on this forum, Thanks!
MAF= mass airflow
lightweight flywheels are notorious for causing misfire CEL codes especially in bugeyes... Also oiled air filters are bad for our already touchy MAF sensors...
 

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Hi,

New here. Just brought my first Subaru as im mainly a Rotary or nissan guy. Anyway I have just brought a 1999 jap import wrx wagon which has a misfire. I have changed fuel filter which has helped a wee bit but my main question is how do i access the fault codes? Do i need a diagnosis tool or something? Also how do i read the fault code?
 

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I don't know how you would go about it on a '99 WRX. I have an access port which can read the codes. But more than likely your nearest Auto Zone will check your CEL codes for free.
 

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I have the 03 WRX, would you recommend the NKG Platinum Spark plugs? I need to replace mine and I think this could be the reason for my misfire codes.
 

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I have the 03 WRX, would you recommend the NKG Platinum Spark plugs? I need to replace mine and I think this could be the reason for my misfire codes.
This is what Subaru recommend. See the owner's manual for the spec.
 

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Hi,

New here. Just brought my first Subaru as im mainly a Rotary or nissan guy. Anyway I have just brought a 1999 jap import wrx wagon which has a misfire. I have changed fuel filter which has helped a wee bit but my main question is how do i access the fault codes? Do i need a diagnosis tool or something? Also how do i read the fault code?
yeah if you have a real jdm 1999 wrx, you will need to get an OBD1 reader, not OBDII. but yeah autozone should be able to read it, if they still have OBD1s laying around for those pre-1996 (USDM) cars
 
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