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Mike V.
Mike V., Nissan Technician
Category: Nissan
Satisfied Customers: 25339
Experience:  Nissan factory trained and Certified Subaru Technician.
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Engine rpms fluctuate while driving, especially when

Customer Question

engine rpms fluctuate while driving, especially when accelerator is released and rpms increase then drop
Submitted: 1 year ago.
Category: Nissan
Expert:  Mike V. replied 1 year ago.

Hi there,

Is the check engine light on?

Does the truck experience low power?
Does it idle smoothly?

Customer: replied 1 year ago.
check engine light is on. scan came up with oxygen sensor code however. seems to idle fine while in park.
Expert:  Mike V. replied 1 year ago.

Ok, can you tell me how long the idle stays high when you let off the accelerator?

Also, do you happen to know the P code you are getting? P0135 for example?

Customer: replied 1 year ago.
it idles a little high/loud on initial start up, but then comes down & sounds normal.
Expert:  Mike V. replied 1 year ago.

Any other info to my questions?
I am asking because a certain amount of idle speed increase when you let off the gas is fairly normal as long as it is brief, like 2 seconds or less.The O2 sensor can cause some of the variation when cruising as well because the computer uses it to change the fuel mixture as you are driving the truck. Initial start should give you a high idle that returns to normal because it kind of defaults a fuel mixture until the computer has a chance to make an adjustment based on the inputs from the sensors.

Customer: replied 1 year ago.
it last for 2-3 seconds, like it is down shifting. no i don't have code just told it came up as oxygen sensor. sensor was replaced twice & check engine light still came back on.
Expert:  Mike V. replied 1 year ago.

I am going to need the code then if possible. If you have a part store nearby, many will check the codes for you at no charge. Sometimes the code is a result and not the actual problem. IF there is an intake leak for example, you might get a code for the O2 sensor. This isn't because the sensor is bad, but because something else is happening with the engine and it looks wrong to the sensor. I feel if you can get this for me I can provide much better assistance.

Customer: replied 1 year ago.
it also does increase or jump(not as often) while driving with accelerator depressed.
Expert:  Mike V. replied 1 year ago.

Ok, this sounds like a possible transmission type of issue. Not to say the transmission is bad, but if the throttle position isn't reporting properly there might be some lag in the shifting. This would increase the engine rpms while driving down the road. Sometimes this can happen without a code for the throttle position sensor. Kind of a flat spot on the sensor itself.

Customer: replied 1 year ago.
got the code. it is P2A03 BANK 2 SENSOR 1
Expert:  Mike V. replied 1 year ago.

Ok, we know the sensor is not the likely culprit here since it's been replaced twice. Assuming of course they are replacing the bank 2 sensor and not bank 1 by mistake. It's more common then you might think.

Anyhow, this leaves the possible issues to be either the fuel pump, the fuel injectors on that bank or possibly intake air leaks.

That being said, since the truck idles good I don't think you have any intake leaks, so I would focus on the possibility that the truck has a fuel pump issue or a problem with one or more of the fuel injectors not spraying properly on that bank. It is possible that what you are feeling at higher speeds is caused by a drop in the fuel pump pressure. This would have to be driven with a pressure gauge on the fuel line to determine if it's the cause or not.

Bank 2 is the driver side, just for clarity. Also, the mass air flow sensor can cause a lean fuel mixture, so the shop that is trying to repair this for you should monitor the input from the mass air flow sensor. If it's out of range it can cause this without setting a code for itself. I have seen this in the past as well.

Please let me know what more I can do to assist you today. Also, please remember to rate my answer, Just Answer does not compensate me for my time and resources. Follow up questions are included in the price of your question. If you are using the free trial, a rating is still required.
Thank you so much!