Nissan Repair Questions? Ask a Mechanic for Answers ASAP
Hello and welcome! My name is ***** ***** I can assist you with your question. The knock sensor will not cause this idle issue you are describing.
This low engine idle or rough running condition is either caused by an air or a vacuum leak or a stuck open EGR valve. I would start by checking for air/vacuum leaks first and then go after the EGR valve. Look close by the intake manifold gakset and throttle body gasket as well as all of the vacuum hoses and lines and replace any as needed.
You can check the signal from the mass air flow sensor. If it is low at idle, this indicates a vacuum leak. The output voltage signal and should read about 1.3 volts at warm idle.
Also, check the throttle body to ensure it is nice and clean and it is not sticking. In addition, check the TPS voltage to be sure it is reading correctly at idle and that the voltage is nice and steady with the throttle plate closed when this idling issue occurs.
And be sure to check the fuel pressure regulator for leaks. Remove the vacuum hose and if there is any fuel present, the regulator is bad and will need to be replaced.
Last but not least, if all checks out good and there is no air or vacuum leaks, then I would suspect a bad/lazy idle air control valve located on the side of the throttle body. They can get slow over time and stick closed resulting in a low idle or stalling condition.
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