my 2004 infiniti g35 coupe shuts off on me shortly after starting, repeatedly. After starting it a few times it would crank but not start at all as if it were out of gas. When the key is turned to acc i noticed the fuel pump does not prime as it would and the radiator fans would come on but the radiator is not overheating or leaking.
I have had both camshaft position sensors and crankshaft sensor replaced (which solved the hard starting and ses light problem I had) and replaced the fuel pump. What could be the problem?
Also the idle goes up and lowers then sometimes goes up again.

 

happens when the engine is cold or warm

 

Sounds like a vacuum leak but hard to tell with an internet diagonals. I would just take it to a mechanic.

 

Check your MAF? I do not know if this would necessarily cause your car to just shut off, but I was having issues with hard starts and my idling being very low. After all the tests, ended up being my MAF. My car would fire right up but then shut right off until it was warmed up.

Finally got a Nissan dealership to diagnose the problem, changed it, and she runs like a champ now.