CEL code P0171 System Too Lean Bank 1

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I'm sorry to hear you're having trouble with your RX300. A P0171 code indicates that the engine is running too lean on Bank 1, meaning the air-fuel mixture has too much air and insufficient fuel. Since you've already replaced two oxygen sensors, the issue might lie elsewhere. Common causes include vacuum leaks in hoses or the intake manifold gasket, a failing mass airflow (MAF) sensor, a clogged fuel injector, or a weak fuel pump. Your low idle and poor gas mileage suggest fuel delivery or airflow problems. Start by inspecting for vacuum leaks and cleaning the MAF sensor, as those are frequent culprits. If those don't resolve the issue, testing the fuel pressure and injectors may be necessary. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!