On my wife's 2004 Lexus RX330 she had Check Engine light on. I checked the error code P0300 , cylinder (s) is misfiring or is randomly misfiring. The car runs smoothly even on idle so no cylinders are dead, but the error persists. Should i check the intake manifold gasket? could that be a faulty fuel injector or spark plug?

 

Clean the errors, have a drive, check for errors again.
What is the mileage? When were spark plugs replaced last time?