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Discussion Starter · #1 · (Edited)
Hello All,

So in my 2011 WRX wagon with 120k, I’ve got a misfire code P0301 and rough idle with roughness counts in the cylinder, will occasionally stall dropping to idle from load, especially when cold. We’ve done/checked the following:

  • all spark plugs new <15k miles
  • new MAF, cleaned
  • new injectors cyl 1 & 3
  • new coil pack cyl 1
  • seafoam through gas tank
  • dealer induction cleaning service
  • soldering in wiring harness fixed
  • ground wire near cyl 1 replaced
  • compression test good - tested multiple times over ~2-3k miles
  • leakdown test good

Next thing my shop was thinking was egr valve or intake/tgv gaskets for that cyl bank. Anyone here have any ideas? I checked the misfire pinned thread and it looks like we’ve tried just about everything. Trying to avoid engine-out or head rebuild, compression/leak down tests all being good points away from that direction.

Any help you all can provide is greatly appreciated.

Super Moderator
10,914 Posts
Check the intake for leaks

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Water.....sometimes waves
1,611 Posts
If it is one cylinder, i'd put a new plug in. Cheap test to ensure that one plug is not the cause.
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