P0300 and p0021 2007 infiniti g35x

Question

if i change the spark plugs the code p0021 will be gone or no

Answer 1

for P0300 thats the first thing to do if you have 100k miles. Also using low octane fuel will cause this problem along with destorying the catalytic converter.

P0021 is for the intake valve timing control solenoid valve, when was the last you replaced the oil? dirty oil will cause this problem along with a bad intake valve timing control solenoid valve, crankshaft position sensor and camshaft position sensor

 

checking the intake valve timing control solenoid valve bank 2 after replacing oil.

 

Terminals Resistance

1 and 2 7.0 - 7.7 Ω [at 20°C (68°F)]

1 or 2 and ground ∞Ω

(Continuity should not exist)