Okay, so I have an 03 nissan 350Z. I got it and the guy I bought it from said it had a bad 02 sensors so it wasnt running great.
The car lacked the power it was supposed to have. White smoke from the exhaust. Carbon build up on PASSENGER side spark plugs and intake. Runs fine in higher gears and rpms but tries dying in lower gears or neutral upon speed reduction. Have to feather gas and clutch to keep running. Throwing code P0300. Random cylinder misfire. I have read everywhere and changed all the things that came to mine but still the same result. Long story short:
Replaced all O2 sensors
Replaced Mass airflow sensor
Replaced all spark plugs/coils
Replaced all fuel injectors
Replaced all fluids
I'm out of ideas

 

Is the car overheating? How bad is the white smoke from the exhaust? Typically white smoke is coolant in the combustion - more specifically (likely) your head gaskets are blown. Perform (or have a shop perform) a compression and leak-down test. This will likely give you an idea what's wrong with the car.

 

The car has Zero heat issues and the coolant levels are consistent, but I will have it done.

 

First thing i would check with a random multiple cylinder miss before changing any parts would be vacuum and fuel pressure. If these 2 values are out of wack no matter how many parts you throw at it will fix the issue.

 

How can I check the vacuum and fuel pressure myself? Do I have to take it to a shop?

 

Compression test

 

most auto parts stores have fuel pressure tester available to rent for free after they are return. Vacuum guage testers are cheap and can be picked up at same stores. Specs can be found by searching with google pretty quick.