P0102 > P0420 Cadence

Maintenance/Repairs
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P0102 > P0420 Cadence

Looking for some insight on recent issues my 2011 Subaru has given. Listing the issues in the order they happened.

-Brought Car in for scheduled oil change, shop suggested new cabin and engine air filter (they most certainly needed to be replaced). I said gave them the go ahead, paid for both. Before leaving got a quote from the shop for new tires, serpentine replacement.

-3 weeks later- Bring Car in for quoted maintenance. When picking up my car the mechanic mentioned exhaust manifold seal not secure/failing, quoted me on replacement and plan on doing it in a few weeks. Specifically asked him if this would have any impact on car. Mechanic told me overall yes but no damage would be done to the car just a loss in performance. Honestly, the car was running great- no lag in in acceleration, sounds like it always has since I got the vehicle.

-2 weeks after maintenance- Come to a stop light and shift into first gear, while idle and clutch engaged engine starts choking out/RPM fluttering. Scream fuck out loud. Keep the engine running by giving it some gas and releasing clutch. Car dies as I made a turn at the light. Starts right back up. On my way home any time at or above 4,000 RPM car is fluttering and boggy. Engine light comes on, code -P0102. Lift the hood and the air intake hose is not connected. Fixed, cleared the code car running great.

-2 weeks after P0102 code, Car performing great- Engine light comes on. Before even shooting the code- lift the hood, air intake hose was connected, make sure the Air filter is in place- Pull out Air filter and it was never replaced (called the shop and they felt dumb as hell and gave me a free oil change, my money back and some other free stuff) The Air filter is beyond clogged and I really want to stress this part. It was beyond screwed up. Not even sure how it got that dirty, as I routinely replace them or have it replaced with scheduled oil changes. Buy a new filter, pop it in, shoot the code, P0420 comes up… Clear the code. Have driven the car ~50 miles since clearing the code and the engine light hasn’t come on.

Given that series of events, is there any possible way that it was the Engine Air filter that triggered the P0420 code? I love this car overall and have done a great job with overall routine maintenance, part replacement, etc. The car does have 113k miles on it, really hoping it’s not the CC.

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Here’s the first things you do . . .

Go drive your car for several miles and let everything get up to proper operating temperature

Put the car on jackstands and let it idle

Get under the car on your creeper

Any exhaust leaks . . . ?

Now get your scanner and monitor the oxygen sensor activity upstream AND downstream

Is the downstream oxygen sensor sensor signal fluctuating like crazy . . . ?!

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My guess, the problem is the exhaust manifold leak. That will allow outside air into the exhaust stream, which will confuse the O2 sensor reading. The result could be an incorrect air/fuel ratio.

BTW, suggest to replace the colorful expletive in your post above to something you’d hear on the Car Talk radio program.

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in addition to the above replies, it might be time to consider a new shop. Or at least a second opinion on the exhaust manifold leak.
the way you are describing things sounds like this shop could be playing some games to get you to return…

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Hi I saw the flag. @boakgerr_187609 i cleaned up the profanity and you’re good to go. We ask folks not use f bombs around here. Hope you get some help with your issue.

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thank you- but ya missed one. :slight_smile:

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