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sprinkles08, ASE Certified Technician
Category: Subaru
Satisfied Customers: 22655
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I have a 91k mile 2009 wrx with a rough idle. vacuum steady

Customer Question

i have a 91k mile 2009 wrx with a rough idle. vacuum steady at 18inhg. spark plugs recently replaced, gapped correctly. intermittent cylinder 2 misfire, not noticeable besides slightly rough idle. roughness disappears when off idle. ign coil for cylinder 2 replaced. no changes in idle when spraying brake clean on any and all vacuum lines as well as intake ducting. fuel trims +/-4% of 0% in all conditions, long term and short term. crank sensor cam sensors waveform shows difference between LH and RH cam signal of about 2 or 3 ms. cannot perform compression or leakdown on cylinder 2, found the spark plug threads in the head to be iffy at best when i removed the old plugs. my current course of action points me at the turbo inlet, throttle body hose, or timing belt tensioner. any ideas?
Submitted: 1 year ago.
Category: Subaru
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

If the problem is only on the number 2 cylinder then the issue is going to be something that just affects that cylinder rather than the timing belt tensioner or another issue that would affect all cylinders.

If spark and a localized vacuum leak have been ruled out then I suspect valve leakage but it's possible that it could be an injector issue. Has the number 2 injector been moved to another cylinder?

Customer: replied 1 year ago.
i fear a burnt valve as well on said cylinder, and i wish i could easily do a compression test and a leakdown.
i intend to replace the throttle body hose and the turbo inlet, in case either of those two are creating some sort of leak that spraying brake clean didn't reveal.
as for the injector, i considered that a possiblity and still do. i will order 2 new ones and replace the LH bank of injectors merely due to the pain of removing and reinstalling injectors.
does it change any matters if i state that this rough idle and intermittent p0302 has been ongoing for about 31k miles with no change for better or worse?
Expert:  sprinkles08 replied 1 year ago.

If it was me I'd swap one from another cylinder to number 2 and see if the miss moves rather than buying new injectors. An injector issue would probably get worse over time but possibly not.