This sounds like a case of fuel vaporizing in the fuel line . This happens when heat shielding is removed and not returned when work is done on the vehicle. I would check the fuel lines near the manifold check the fuel rails have all proper shielding in place. I would also check for exhaust leaks that could be heating fuel lines under the car. Just something to look for . you may also want to try cycling the fuel pump a couple of time before attempting to start the car. This is done by turning the key to the point the idiot lites come on but not turning over the motor . You should hear the fuel pump hum when it stops humming, 5 second or so, turn the key to the off position then do it again . This pressurizes the fuel rail . If the pressure is dropping off then the vehicle will be hard to start . Hope this helps