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Discussion Starter · #21 ·
P0172 is too rich, injectors clogged would be too lean. Could be a stuck open injector. Theoretically, a bad spray pattern could maybe cause inefficient burn and misfiring, which would cause it to be too rich. But you'd have misfiring.

I'd give the map a check. Maybe EGR? Computer thinking it's putting in less EGR gasses into the intake than it really is? That would do it. Has the EGR plate and passages been cleaned?
Thanks @Phantom Z3
I might have misfiring. I don't have any audible misfiring, but I'm struggling with another issue of the car violently surging/bucking when I slightly let off of the accelorator (even in VTEC mode, when lean burn is disabled). Part of me wonders whether that surging/bucking might be misfiring. EGR valve has been replaced, EGR plate and passages have been cleaned. And I've followed all of the troubleshooting in the service manual for a P0172.
 

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Why wait? Install the spacer now, and if the code stops, it worked.

My theory is that all of these cat/O2 codes are related, and you can't tell what's really wrong. The spacer is quick, cheap, and easy, and if fixes a lot of them. I always start there.

Sam
 
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Why wait? Install the spacer now, and if the code stops, it worked.

My theory is that all of these cat/O2 codes are related, and you can't tell what's really wrong. The spacer is quick, cheap, and easy, and if fixes a lot of them. I always start there.

Sam
Isn't the P0172 code related to the first O2? On other cars, the second O2 works to check on the cat, nothing more. You can unplug it and it should work fine. All the "unfouler" does is prevent the secondary O2 from reading wildly up and down meaning the catalytic converter is on its way out since the cat is supposed to burn off extra fuel and reduce other emissions. On non-Lambda sensor cars, it burns rich and lean up and down on purpose "hunting" for the target air fuel. And you'll see the "hunting" on the second O2 if the cat is bad.
 

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These codes don't always mean what they say. I'm just telling you where I would start. If it doesn't work do something else.

Sam
 
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