bankyb

I need help with my 2001 RX 300. I have to crank it more than once before it starts. It runs smoothly though once its started and it has no other observed issue but for the multiple cranking for it to get started. The only recent thing I did on the car before this cranking issue started was a change of my Oxygen sensors and Air flow sensor because of issue of black smoke and bad gas mileage after fuel got finished in the tank. The black smoke and related issues have resolved and the only present issue is just the multiple cranking to get it started. While I was having the black smoke issue, there was not mutiple cranking to get the car started issue. The "hard starting" issue started after the smoking issue was sorted out. Please, does anyone have any advice on this?