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I fail to see how the cats would be commanding the computer to pull fuel, specifically at idle. O2 switching is really solid. If anything, it should be seeing a lean condition because of the increased airflow since these cats are not near as dense as the factory, not a rich condition. I don't see how there'd be any difference between aftermarket cats (it's not throwing an in efficiency code) and higher flow shorty headers. Like I said, IF anything, it's an incompatibility with the Bosch O2 sensors I installed. However, I believe the factory sensors were partially dead since they never picked up on the leaking injector on cylinder 8, or at least slow to respond. Once the new o2 sensors were installed, they immediately picked up on the fueling imbalance.Aftermarket cats have a long and well earned reputation for this type of issue.
What kind of catalytic converters are they?