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Discussion Starter #1
I discovered that my o2 sensor plug had fallen out one day so bought and installed a new one, this fixed the wrx boxer like engine sound coming out of the exhaust and temporarily turned off the check engine light. Unfortunately this only lasted for a couple miles of driving before the sound and CEL returned. I've made sure to tightly secure the plug but every time I start the car up it sounds fine for 5-10 minutes then the engine starts making the noise again.

I'm not entirely sure if I should be driving my car with the engine performing like this. When stopped it idles low enough to the point where it starts to shake briefly then picks back up. The CEL also switches from just staying lit to flashing. Is this a problem not related to the o2 plug? Anyone have any ideas on what it could be?
 

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What are the codes?

Also....what do you mean the "plug" fell out. Do you mean the harness came unplugged, the o2 sensor came out, or a bung plug fell out? Idk how an o2 sensor can come unplugged at the harness, but i guess its possible. Check real good that no wires are burned or something.

You can get the codes without a scan tool. I can post a how too link if you need me to.

You may need to replace the o2 sensor. You may need to replace the other side of the harness. You may not have a good connection. But it would help to know what your codes are just in case there are non o2 related codes.
 

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http://www.b15u.com/threads/206-OBD-II-Codes-List-amp-Clearing-Codes

There is how to check your codes.


Still confused on what you replaced. You could have meant the plug, the pigtail, the sensor, or just a bung plug. Probly need to fix whatever allowed it to come unplugged. I suspect you still have a poor connection. But check your codes and post them on here.

Could also have an exhaust leak or something. Sometimes they won't leak until the exhaust is hot.
 

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What are the codes?

Also....what do you mean the "plug" fell out. Do you mean the harness came unplugged, the o2 sensor came out, or a bung plug fell out? Idk how an o2 sensor can come unplugged at the harness, but i guess its possible. Check real good that no wires are burned or something.

You can get the codes without a scan tool. I can post a how too link if you need me to.

You may need to replace the o2 sensor. You may need to replace the other side of the harness. You may not have a good connection. But it would help to know what your codes are just in case there are non o2 related codes.
http://www.b15u.com/threads/206-OBD-II-Codes-List-amp-Clearing-Codes

There is how to check your codes.


Still confused on what you replaced. You could have meant the plug, the pigtail, the sensor, or just a bung plug. Probly need to fix whatever allowed it to come unplugged. I suspect you still have a poor connection. But check your codes and post them on here.

Could also have an exhaust leak or something. Sometimes they won't leak until the exhaust is hot.
Thanks for the link, was unaware of that code checking method, so I ran the check and it looks like the code is P0300 (Random/Multiple cylinder misfire detected), 10 slow blinks, 3 fast blinks followed by two more sets of 10 fast blinks.

When I say the plug fell out I mean that I had a previous o2 sensor plug covering the welded bung on the exhaust that must have come loose and fell off. There is a possibility that I did actually have a o2 sensor instead of the o2 plug but it's been so long that I truly can't recall, furthermore I removed my hotshot headers many years back which further reinforces the fact that there was no o2 sensor rather than a o2 plug. Does that code seem accurate for my current predicament?
 

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Discussion Starter #6
Well if it was fixed for the minute after you "plugged" w/e you it was, then you're probably on the right track.

Sounds like an exhaust leak to me, at least the wrx sound. Or a misfire.
I was thinking of an exhaust leak myself as the sound is similar to when I had an opening between my exhaust year back. After finding the misfire code I'm a little confused on what it could be.
 

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Need to sort out that code before anything else. Search P0300 at the top of the page.

And yeah an extra o2 bung with a bung in it is normal. Thought maybe you meant the bung plug came out. You could have an exhaust leak, BUT fix the p0300 first. An exhaust leak wouldn't cause that code. Well......"maybe" if you had a leak before the primary o2 sensor, but I would expect to see additional codes if that were the case.
 

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Discussion Starter #8
Need to sort out that code before anything else. Search P0300 at the top of the page.

And yeah an extra o2 bung with a bung in it is normal. Thought maybe you meant the bung plug came out. You could have an exhaust leak, BUT fix the p0300 first. An exhaust leak wouldn't cause that code. Well......"maybe" if you had a leak before the primary o2 sensor, but I would expect to see additional codes if that were the case.
To sort out the p0300 code it looks like I'm going to have to go by process of elimination unless I take it to a mechanic? After searching some threads on it, it sounds like it could be ignition coils since my car was having trouble starting up recently even before this incident. I didn't see in that pedal dance code checking thread to check how you would tell if multiple codes would pop up, unless each additional code would result in different sequences at the start of the slow flashes indicating the start of the code.
 

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Yes that's all correct. Lots of different things can cause that code. And yes if you have multiple codes they flash one right after the other as you described.
 

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Mechanic is just gonna guess as well. They might have more educated guesses, but maybe not. That can be a tough code sometimes. You might get it right away though. Harder to diagnose when its just that one code.


If it was a single cylinder missfire it would be way easier to diagnose and fix. I would think its not a coil since its multiple cylinders.
 

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Yes that's all correct. Lots of different things can cause that code. And yes if you have multiple codes they flash one right after the other as you described.
Mechanic is just gonna guess as well. They might have more educated guesses, but maybe not. That can be a tough code sometimes. You might get it right away though. Harder to diagnose when its just that one code.


If it was a single cylinder missfire it would be way easier to diagnose and fix. I would think its not a coil since its multiple cylinders.
Good point on the multiple cylinders, ill keep digging for the fix, thanks a lot for your help, it's much appreciated!
 

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Discussion Starter #14
Could be something as simple as a disconnected coil pack, or damage to the harness, maybe a coil pack needs replacing. Try swapping them around and see if a new cylinder has the problem (make sure you mark them so you know which is which)
When you disconnect the coil packs do you just unplug the plug or do you have to pull the coil pack out of the hole? You mentioned swapping them so put each one in a different slot?
 
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