Answer received from Repair pal was there could be a vacuum leak at the intake manifold. Need to know where the air flow meter is on the car.
Where is the air flow meter located on a Lexus RX300 ? on 2000 Lexus RX300
It is located in the air filter housing. Its retained with two small philips screws and has an electrical connector with about 4 or 5 wires on it in one connector.