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Old 05-12-2021, 03:55 PM   #1
Lega-C
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Member#: 524256
Join Date: May 2021
Chapter/Region: BAIC
Location: CA
Vehicle:
2006 Legacy 2.5i
Silver

Default Misfire/rough idle after replacing vc gasket, spark plugs and wires

2006 Subaru Legacy sedan 2.5i 4AT

Was driving home the other day and my car started sounding like a 2 stroke. Got the codes ran and it was a plethora of P0301, P0303, P0076, and P0420. The P0076 had been an issue for a while but the only symptom was a CEL and cut off at 4K (car refused to rev past 4K). I replaced the spark plugs. While doing so found a lot of oil in the wells so I did the plugs and valve cover gasket as well. Was putting it back together when one of the wires broke so I replaced all of those as well. Got everything back together and I still have a misfire. I’m thinking it could be a vacuum leak or a bad MAF. I may be missing a few codes but I’ll update with the full list when I get a chance to read them again. Any help is appreciated!

TIA
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Old 05-12-2021, 05:03 PM   #2
serrilion
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Member#: 348982
Join Date: Mar 2013
Chapter/Region: NESIC
Location: Shoreham, VT
Vehicle:
2002 TS
Multi

Default

How many miles are on the car? Headgaksets en such been checked?

Many things cause misfires...

Your coilpack could have gone bad causing the car issues, thought you have new plugs and wires, the coil it self could be the trouble maker.

The codes though point me toward a plugged catalytic converter

Does the car have any strange smells out the exhaust pipe while its running?
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Old 05-12-2021, 05:03 PM   #3
serrilion
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Member#: 348982
Join Date: Mar 2013
Chapter/Region: NESIC
Location: Shoreham, VT
Vehicle:
2002 TS
Multi

Default

How many miles are on the car? Headgaksets en such been checked?

Many things cause misfires...

Your coilpack could have gone bad causing the car issues, thought you have new plugs and wires, the coil it self could be the trouble maker.

The codes though point me toward a plugged catalytic converter

Does the car have any strange smells out the exhaust pipe while its running?
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Old 05-12-2021, 06:13 PM   #4
Lega-C
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Member#: 524256
Join Date: May 2021
Chapter/Region: BAIC
Location: CA
Vehicle:
2006 Legacy 2.5i
Silver

Default

I believe the p0420 is just being caused by the excess unburnt fuel from the misfire. As for head gasket I have not checked. I don't think it's an issue despite the fact I've lost some coolant since I last filled it (a year ago). No smoke from my exhaust or coolant in my oil. I'm trying to work my way backwards to do the least expensive solutions first. P0076 is for "Intake Valve Control Solenoid Circuit Low (Bank 1)", could this cause a misfire?
As for smells/smoke there was a small amount upon start up after doing the plugs, wires, and vc gasket but I think that was from it burning off some oil that got in the cylinder heads when I took out the spark plugs. There was a smell To the exhaust but it just smelt rich, not like sulfur or burning coolant.
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Old 05-12-2021, 08:33 PM   #5
Lega-C
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Member#: 524256
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Location: CA
Vehicle:
2006 Legacy 2.5i
Silver

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I forgot to mention it has 194k miles on it.
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Old 05-13-2021, 11:49 AM   #6
Lega-C
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Member#: 524256
Join Date: May 2021
Chapter/Region: BAIC
Location: CA
Vehicle:
2006 Legacy 2.5i
Silver

Default Update

Ran my codes again and I got rid of the P0420 and P0301, so now only a misfire in cylinder 3. I pulled each plug wire individually and the only one that didn’t drastically drop idle was 3. Pretty confident it’s the ignition coil. Got a replacement and will be putting in this morning. When I had my codes read both 02 sensors went off with p0113 and p0132 but I’m assuming that’s just from the misfire. Also had a p0102 pop up so I replaced the maf sensor. So all in all I think the new coil should clear everything up. Wish me luck!
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Old 05-22-2021, 02:39 PM   #7
serrilion
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Member#: 348982
Join Date: Mar 2013
Chapter/Region: NESIC
Location: Shoreham, VT
Vehicle:
2002 TS
Multi

Default

Ever get a solution to it? Also it will smell rich if 02 sensors are off as they are flooding the motor trying to save it. If a cyl is not firing in this case #3, its fuel is simply being pushed threw the exhaust valves and could be why the sensors are freaking out a bit.

Let us know how it goes
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