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Discussion Starter #1
I have a '04 WRX, 31k miles. 100% bone stock

I've been throwing a CEL for about a month now and finally got around to scanning it because it started to idle funny. Here are the codes:

P0546 - Exhaust gas temperature sensor circuit high input
P0303 - Cylinder 3 misfire detected

I did some research on each code but I was unable to find a correlation between the two codes (maybe it's two separate problems?) Also it seems the P0546 code typically only applies to aftermarket exhaust and my WRX is completely stock. If anyone has any ideas of what might be going on (before I start tearing out potential bad parts) I'd appreciate any advice and input.

Thanks in advance
 

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When you got the ECU scanned did they clear the codes and reset the ecu?
 

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I bet your coil pack came unpluged. I would check that. Search a spark plug install tutorial.
Sorry, I have to say this. You post on lots of threads in this section and usually post responses that show your lack of car knowledge. Go ahead and hate me, but somebody had to say it. People will respect you more if you stick to what you know. Your answer makes it obvious that you don't know what a coil pack is or how it works. A coil pack has a connection coming out of it for each cylinder. If the plug for cylinder 3 had come unplugged, the OP would have said a lot more than it isn't idling right. The engine would be in some serious distress if only 3/4 cylinders were firing. If the incoming plug had come out, the car wouldn't run period. Sorry I had to say it. :sadwave:

A cracked coil pack could cause the behavior the OP posted, but normally it isn't going to start out of nowhere. Something would have to cause it to crack. You could check it for cracks just to make sure. A loose plug on the pack could cause it, but that's unlikely since you're really not going to get a loose plug. On a coil pack, normally either the plug is in or it isn't. I would start by checking the most simple thing, the spark plugs. When was the last time they were changed? If never, then the misfire may be caused simply by a dirty plug. When was the last time the air filter was changed? The oil? Misfires are going to be caused by a lack of air, fuel, or spark, or possibly too much fuel. Normally it's a spark problem though since an air or fuel problem will normally show up in more than one cylinder. A clogged injector is about the only thing that will cause a misfire in only a single cylinder. The exhaust gas code is likely separate, but you never know. I would start by fixing the misfire code and then looking at the exhaust.
 

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It sounds like the EGT probe in the up pipe has simply failed or isn't making a good contact.
 

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Discussion Starter #7
Thanks for the replies guys. The air filter and oil were changed within a month.

I think I'll do a spark plug and wire swap to start off. They're the original set and to be honest I didn't think it would be the plugs after only 30k miles, but I agree that's the quickest and easiest test to do.

Thanks again.
 

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Thanks for the replies guys. The air filter and oil were changed within a month.

I think I'll do a spark plug and wire swap to start off. They're the original set and to be honest I didn't think it would be the plugs after only 30k miles, but I agree that's the quickest and easiest test to do.

Thanks again.
The WRX's are coil-on-plug.No spark plug wires:).I wouldn't spend the money on new plugs.Just check the gaps.Miss fires can be associated with bad/sticking injectors.Try reseting the ECU first and see if the codes comeback.I would definatly pull the EGT probe and see if its still in one piece.Try running some injector cleaner and changing the fuel filter if the missfire code comes back.
 

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Discussion Starter #11
The WRX's are coil-on-plug.No spark plug wires:).I wouldn't spend the money on new plugs.Just check the gaps.Miss fires can be associated with bad/sticking injectors.Try reseting the ECU first and see if the codes comeback.I would definatly pull the EGT probe and see if its still in one piece.Try running some injector cleaner and changing the fuel filter if the missfire code comes back.
Sounds like a plan. Hopefully some of the above simple solutions will work. I really appreciate the help.
 
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