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P0420 indicates a lack of efficiency in catalyst BANK 1. Most of the time, she's been missing for a while, but then she's back. At this, idling speed starts a little bit, the machine is becoming a little "thoughtfully".
The first thing to do is check the catalyst condition. If he's okay, it's probably a problem with one or more fuel injectrs. We need to clean them up on a special stand and check it out. If some of them do not provide the necessary performance, replace them.