I have a 2000 Lexus RX300 with the check engine light on reading a PO171 Bank 1 system too lean code…

I have a 2000 Lexus RX300 with the check engine light on reading a PO171 Bank 1 system too lean code. When I look it up, it could be several different things. It also seems to be burning more gas than it should. What should I start replacing first?

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