p0300 and p0021 codes whats next?

Question

06 nissan frontier. 4.0. i have checked everything on the list and can not find anything wrong. could it possibly be the air fuel ratio sensor(oxygen sensor). need help!!

Answer 1

 

These are the main causes:

Improper spark plug

Insufficient compression

Incorrect fuel pressure

The fuel injector circuit is open or shorted

Fuel injector

Intake air leak

The ignition signal circuit is open or shorted

Lack of fuel

Drive plate or flywheel

Air fuel ratio (A/F) sensor 1

Incorrect PCV hose connection

 

did you try to disconnect one coil at a time while the car is running and see if there is a change in the cars RPM? Check for a intake leak also by spraying brake fuild near the intake and intake manifold and see if there is an RPM change