P0300 is Random/Multiple misfire detected and you can thank your friends at CARB for such wonderful regulations!. It is a two trip fault; it must happen twice during your run period but will set the fault as soon as the second event is detected. It's not clear what year car you have so the misfire detection systems are somewhat different for the various generations. Misfire detection should be disabled at fuel cut-off so that shouldn't be a problem. If someone is having issues with misfire detection my first recommendation is always to clear TEC (Tooth Error Correction - basically adaptive learning of the crank position edges for your particular engine and system) and then re-learn on the road. Your dealer will have to clear TEC but you should be able to re-learn on the road by driving moderately to about 4000 rpm in second gear and then coasting down to 2000rpm with your foot completely off the accelerator pedal. Perform this maneuver a couple of times and that should do it. Assuming you really don’t have some sort of misfire going on, this usually takes care of false detection. Hope this helps!
