Ok, if no codes, then do the basics.....
When it won't start/stalls, have a can of carb cleaner handy.......when the car won't start, spray some carb cleaner into the intake.....if the car almost starts or starts and then dies, then you have a fuel delivery problem...either the injectors are not firing, or there is insufficient fuel pressure....
If it still doesn't start, or almost start, then check for for spark on all cylinders.....