Surging AFR at idle, p0300

[sparetire8]

Hello all. The other day completely out of nowhere, my car has started to idle and drive very rough. The car is running lean with the afr going up and down from 15-20 at idle. I’m confused because the night before it happened the car was running like a dream. It’s a ‘22 GT A10 with catless LTH and corsa extremes (no tune). I’ve been running this setup since last april with no issues up until now. I’ve also had a p0141 code since forever but it hasn’t really gave me problems. I’m led to believe it’s my o2 sensors failing but i’m not entirely sure. I don’t have any other codes besides p0300 and p0141. No CEL as well. Looking for any and all insight anyone could provide. Thanks for reading

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[SheepDog]

More likely a vacuum leak. Look for cracks on the intake tube, loose connections or clamps, anything that has to do with the intake manifold, after the MAF sensor where the engine could be sucking in unmetered air

less likely but still possible is a failure of one of the VVT solenoids

 

[sparetire8]

More likely a vacuum leak. Look for cracks on the intake tube, loose connections or clamps, anything that has to do with the intake manifold, after the MAF sensor where the engine could be sucking in unmetered air

less likely but still possible is a failure of one of the VVT solenoids

My vacuum meter stays at a steady 20-21 at idle. However I’m not entirely sure if that’s normal or not. I examined most of the engine bay and no found no leaks. No sounds etc.

 

[SheepDog]

My vacuum meter stays at a steady 20-21 at idle. However I’m not entirely sure if that’s normal or not. I examined most of the engine bay and no found no leaks. No sounds etc.

It would have to be a big leak to effect the vacuum gauge, and wouldn't need to be very large to upset the AFR.

The best way to check, (if you don't see or hear anything obvious) is with a scan tool and a can of carb cleaner or brake cleaner. You look at the STFT's, while you spray short bursts of cleaner around various areas on the intake, intake manifold. If you see the trims go negative, this indicates that the engine sucked in the cleaner, the O2 sensors read the additional "fuel" in the exhaust stream, and the PCM pulls fuel momentarily.

One issue with running no cats without a tune, is that the rear o2's do play a part in fueling, so if they aren't seeing a change from what the front sensors register, the fuel trims can drift.

Remove the MAF sensor from the housing and make sure there isn't dirt on it, or a bug or something

 

[sparetire8]

UPDATE:

Turns out it was my bank 1 upstream o2 sensor that went bad, covered in soot. Replaced it with DY1442 and the problem disappeared. Also replaced my plugs while I was at it. Thank you guys for helping out

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