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Jay, Nissan Technician
Category: Nissan
Satisfied Customers: 20502
Experience:  20+yrs experience with Nissan & Infiniti Trained & Certified.Currently still working for Dealer
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Just replaced o2 sensor, now car won't idle without dying on

Customer Question

just replaced o2 sensor, now car won't idle without dying on me.
JA: Have you located all of the vehicle's oxygen sensors? Are the wires leading to and from each intact and in good shape?
Customer: I've only replaced the o2 sensor near the radiator in the front of the engine bay. Wiring appears to be in good shape
JA: What is the model/year of your Nissan?
Customer: 2006 Nissan Sentra SE, 1.8L engine
JA: Are you fixing your Sentra yourself? What have you tried so far?
Customer: attempting to lol. So far, the only thing that I've replaced is the o2 sensor based on the c.e.l. codes the ECU spit out at the local autozone.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I was experiencing a previous issue with engine power and performance, but it was tied to rear LED brake lights. That's cleared up and car was good to go prior to o2 sensor change.
Submitted: 1 month ago.
Category: Nissan
Expert:  Lou P replied 1 month ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P replied 1 month ago.

first off to see if the new sensor is the issue, lets unplug the sensor and start the car.

also in order for us to help you the best we can , I need to know as much about the car as possible and the issues you have had and fixed and add ons that you did.


Customer: replied 1 month ago.
Thanks Lou! I know that with most o2 sensor replacements the ECU needs time to "relearn" the mixtures and all that, but this car won't idle long enough to get up to normal operating temperature so I'm not sure what to do. As far as previous issues, not much other than a kind of odd one that's already been figured out, and the current issue.
Expert:  Lou P replied 1 month ago.

ok cool, then lets unplug the sensor, sometimes after market sensors are not wired correctly so it may be draggin down voltage of the ecm, so lets take it out of the equation.

Customer: replied 1 month ago.
Sure, hold on a sec... alright, disconnected the o2 sensor, started the car - same result.
Expert:  Lou P replied 1 month ago.

ok so the o2 sensor is not the issue.

Expert:  Lou P replied 1 month ago.

is the engine misfiring when running or just a super low idle and wanting to die?

Customer: replied 1 month ago.
describe "mis-firing"? The entire engine is shaking 5 sec after start. Sometimes it finds the idle at about 800 RPMs, but only for a second or two before bottoming out in RPMs and dying. Other times, it will hold on at 100 RPMs, and try to stay alive but that's when the engine is shaking and eventually it dies then too.
Expert:  Lou P replied 1 month ago.

ok let me opt out.


Expert:  Jay replied 1 month ago.

Hello my name is ***** ***** thank you for your question.

Does it only shake when first started after the vehicle has been sitting? Also, what codes are you getting exactly?

Customer: replied 1 month ago.
Last night I was able to "feather" the gas pedal, and by keeping the RPMs higher it eventually was happy at idle, but after putting it into gear I had to constantly play with the throttle to keep it running, and if I ever pushed down too far on the gas pedal the RPMs would bottom out. If I let off the gas, idle would return and I could try to go again. Put about 4 miles on it like this hoping to get the engine up to normal temps for the o2 sensor to pull it's settings, but when I went out this morning to start it up, I'm back at square one. Thought maybe it might be the fuel pump relay, but I'm having trouble locating it.
Expert:  Jay replied 1 month ago.

Do you have a Service Engine Soon light when the car is running? If so, do you know what codes you have? Does it get better as the car warms up?

Customer: replied 1 month ago.
I'm not getting a CEL at this point. I had one that identified the o2 sensor, which is why I replaced it. These new problems arose after that. Currently, I can't get the car to "warm up" because it won't stay running, even at idle in Park, for more than a few seconds before the engine dies. I was able to pulse the gas pedal last night, which got it to stay running, but after about 4 miles of constantly doing that my leg was dead. After that, it was idling ok, but did die and require a jump this morning. After the jump, Problem is still there and hasn't improved at all.
Expert:  Jay replied 1 month ago.

The only thing that that sounds like is that maybe the Mass Air Flow sensor went bad. That can cause what you are describing. The MAF sensor when it fails, it fails so it doesn't meter air properly but does not throw a code cause it still runs.

Customer: replied 1 month ago.
Should I be checking relays, or just go pick up a new one? Is it relatively easy to install?
Expert:  Jay replied 1 month ago.

I would use a scanner to monitor fuel trim. A trick to verify the MAF sensor is to unplug the MAF sensor and start the car. If you can watch the fuel trim drop to the default readings of -25% or 75% short term fuel trim, that means there is no vacuum leaks and that the MAF sensor is not metering air properly

Customer: replied 1 month ago.
a scanner... If I'm on my way to Autozone to pick one of those up, what should I refer to it as? Where do I hook it up to to monitor fuel trim? Also, how do I use this if the engine wont stay on for more than 60 sec? is the reading that quick?
Expert:  Jay replied 1 month ago.

Well, if you unplug the MAF sensor and the car will start and idle, that is also another way of possibly verifying a bad MAF sensor

Customer: replied 1 month ago.
okay, let me try that. Ok - so it's idling now, but won't go past 2500 RPMs.. is that normal with the MAF Sensor being unplugged?
Expert:  Jay replied 1 month ago.

Yes.. Unplugging it will only allow it to run only so much. It's not meant to be driven like that, only for testing

Expert:  Jay replied 1 month ago.

But if it's running ok with it unplugged, that is most likely the issue. Make sure you get the part from the dealer. After Market ones never work right

Expert:  Jay replied 1 month ago.

If you have any more questions on this, please feel free to ask.

If not, and you're satisfied with my help, please RATE me by clicking the STARS on top of the page. That is how I get credit for my work. I hope I have provided you with Excellent Service.

Thanks Jay