The check engine light is on already changed the cam shaft sensor and throttle body gasket

Fuel injectors need replacing, can also be a leaking inlet manifold gasket , however check basics first like Clean throttle body first , then replace fuel filter

Sounds like. MAP sensor or cam sensor. You didn't say if Chechen engine light is on. No light on check throttle. body and TPS . it may be loose.

Have you checked for vacuum leaks ?

Spray a small amount of starting fluid around all suspected areas and if it revs up that's where you leak is.

There is a throttle valve positioner sensor located at the end of the throttle valve shaft on the right hand end of the shaft, the sensor then bolts to the throttle body as you face the engine from the front. A defective sensor will set the check engine light and give hesitation during acceleration.

Have u checked the cadeletic converter. It can do funny things

code p 0300 is random/ multiple cylinders ----misfires detected ===causes ---spark plugs ---HT lead/s---injector/s---ignition coil/s---low compression---wiring
he has changed a lot for nothing
a 5 year old engine can have a lot wrong with it --so new out of a crate is no guarantee
most misfires are from injector problems
it could be a loose valve seat insert so have a compression test done if moving the injectors to new locations doesn't move the misfire

it is possible the engine to have a vacuum leak,**** air,or the temperature sensor not to work properly and give wrong message to PCM as cold start. clean also the throttle body from any dirt.

might the engine is sucking air or if it has a stepper motor and is not working.

I had a similar problem - took it into 'Nissan Professionals' and they changed everything you did as well, and had no luck. After 4 or 5 times working on it, they told me that it was a 'loose wire' that had to be re-soddered and then the problem was fixed. I don't know where the wire was, but they made it sound like it was in or around the fuse panel under the hood.
I hope this might shed some light on the problem.

I replaced the Cam Shaft Sensor. I also cleaned the Throttle Body with carb cleaner. I had my wife hold down the accelerator, while running I sprayed down the throttle plate and the entire area around it. Now my TB finally idles smoothly, and it hasn't died yet!! Check engine light is gone and I passed the emissions test!! Yea!!!