Hi all I just purchased a 2005 infiniti g35 sedan. I'm new to the whole vq world. So for starters when I got the car it had a cel for misfire in cylinder 1 and 4 also vvt solenoid and camshaft position sensor both driver and passenger side all of those codes are gone I fixed them. Now the entire time the car had and still has a rough idle and hard time to start up. I did clean the maf and throttle body with no change. Also I have replaced the spark plugs and coils even the injectors all oem and still no change I noticed smoke coming from the motor around the valve cover and behind the plenum but it doesn't overheat I'm stumped because I don't know what else I can do or if the motor is just trash and the weird thing is it immediately begins to smoke at the cold start. Could anyone chime in?

Clean the MAF, do the idle air recalibration. That's a good place to start.

Just to verify you have NO CODES right now yes? And you scanned to check for single trip/hidden codes yeah?

Yeah all the codes are taken care of. Also I cleaned the maf countless times already same with idle recalibration it doesn't do anything.

Next step pull and inspect plugs, compression test, smoke test intake plenum for leaks. OBD2 real-time scan STFT both banks, O2 sensor for proper cycling.

Is there any change when you turn the steering wheel and/or turn on the AC compressor?

Are you pedal dancing the idle air recalibration or using NDS2 ?

Spark plugs were oil free. Electrode was light grey on all of them. Haven't done a compression test but I do hear hissing when it's being ran. Also the metal gasket on the plenum was covered in oil and curved not flat. No zero change when steering wheel is turned and same with ac compressor no change.

Find the hissing, probably a vacuum leak. From the intake tube there's a hose that goes to the left side valve cover directly below the throttle body, the the two valve covers connect with a crossover tube at the front of the engine below the plenum, then the right side valve cover has the PCV valve that goes up to the front of the intake plenum. These things are all readily accessible. Only other vacuum line is the brake booster line which is very self explanatory.

Lastly remove the intake tube and check the corrugated flexible section thoroughly for any cracks.

Sounds like you had removed the intake plenum, make sure you didn't pinch the rubber oil fill/spill in it, that's an INCREDIBLY common mistake.

Ok so the dying has been fixed but it now has blue smoke coming from the exhaust and a check engine light came on for p0300 and p0304. Crazy enough I already replaced spark plugs, coils even injectors are brand new. So I'm going to take the wild guess that the piston rings are done. Cause I did a oil change and the oil was not milky it looked as it should. Coolant is the same so I'll probably just get a new motor.

So it looks like the P0304 is recurring. Check the harness connections (continuity test?) to the coils and maybe swap that coil with one next to it. Nissan likes to use sub-harnesses, which adds electrical connections to make bad contact.
Also, its very easy to mix the coil connections on cylinders #4 and #6. Only reason I mention that is that you have P0300 too.
P0300 can also be caused by vacuum leaks like Cleric mentioned. Check the intake hoses for cracks and all the hoses running to the plenum (PCV, evap hoses, boots, MAF housing)
I've had good luck with letting marvel mystery oil soak in the cylinders overnight to help free up sticking rings. It helped with my Honda that previous owner had run very long oil change intervals.

Its crazy you mention marvel mystery oil. I forgot to mention this g35 I purchased has been sitting since 2017 and barely was turned on when I bought it acc to previous owner. I'm about to add in some amsoil flush let it do it's thing and see what happens. Also the #4 and #6 plugs aren't mixed matched I read here on the forum a guy gave the wire colors I triple checked they are plugged into the correct cylinder.