Q: Vehicle is difficult to start sometimes; Sounds like it's about to stall when at idle

In order to isolate the hard engine start the first test will need to be a fuel pressure and leak down test to see if the pressure is within specifications when the key is turned on and the pressure stays up when the key is turned off. If the pressure drops to zero when the key is turned off then you have a leaking fuel pressure regulator or fuel pump. The fuel rail return line will need to be clocked off to isolate the fuel pump to see if it still leaks down. If it does leak down then the fuel pump internal check valve is bad and fuel pump needs replaced if the pressure now stays up and does not leak down then the fuel pressure regulator has a leaking pressure seat and needs to be replaced.