# 2009 Sentra starting problems - SOLVED ISSUE



## Nissan0301 (11 mo ago)

I have a 2009 Nissan Sentra 2.0L. Recently when starting immediately after starting it surges between 500-1800 rpm and if I don't burp the gas pedal it will die. Once it's warmed up though I have no issue, it starts smooth and idles normally, drives normally. I cleaned the MAF but no difference, new air filter. There is a slight discoloration on the shiny part of the MAF, not sure if that mattered.

I have a new MAF on the way (possibly the intake air sensor since it's combined with the MAF) Any other sensors I should check out? 
Possibly the Coolant temp sensor?


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## VStar650CL (Nov 12, 2020)

If your ECT was malfunctioning you'd see it on the dashboard, an '09 only has one and not separate sensors for cluster and ECM like older Sentras. The Intake Air Temp (IAT) Sensor could be acting up, but that's part of the MAF assembly. I doubt the MAF itself is causing your issue, unless maybe it's badly out of calibration. Have you tried doing an IAVL to recalibrate it?

You really need to put a streaming scanner on it and check out the IAT reading and fuel trims to see what's going on. Blindly throwing parts at it is likely to be a vain exercise.


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## Nissan0301 (11 mo ago)

No I have not. I think I'm going to try that first.

I saw the resistance can be checked for the IAT so I'll do that as well to see if it's within spec. Thanks

by the way, I don't have any check engine codes.


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## Nissan0301 (11 mo ago)

I did the intake air volume learning and it did not help with the problem. I won't be able to throw a live data obd2 on there until end of March.

When in D, foot on the brake waiting at a stop, it stumbles from 750 to about 500 rpm and then reverts back to 750-800 all within a period of about 3-5 seconds. Not all the time but a couple times during a 30 minute drive. It doesn't do it when driving but idling with it in D and foot on the brake.


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## Nissan0301 (11 mo ago)

I'm trying to test the IAT sensor but the manual from this site says to test between pin 5-6 and mine has only 5 pins on sensor and plug?


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## VStar650CL (Nov 12, 2020)

That's the right info for an '09 Sentra, should be 6 pins with the IAT signal on 5~6 for all variants. The only difference between the MR20 and QR25 is the color of the ground on pin 6, it's Orange on the MR20 and Black on the QR25. Just about all Nissans from the 00's have 6-pin MAF's, so I'm not sure if your car info is wrong, you're looking at the wrong part, someone modified your car, or a wire is broken off and you're simply not seeing it.


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## Nissan0301 (11 mo ago)

Well just call me confused.

the new MAF on the way is 5 pin as well. The harness is 5 pin also.


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## VStar650CL (Nov 12, 2020)

That's a 6-pin shell, pin #1 is open. Most of them are set up that way.


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## Nissan0301 (11 mo ago)

Alright, thanks. I'll get to testing then.


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## Nissan0301 (11 mo ago)

I have my live data reader coming Monday. I'll be able to check the fuel trim then and report back.


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## VStar650CL (Nov 12, 2020)




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## Nissan0301 (11 mo ago)

Got the reader. It looks like at idle the STFT is -4.7 and as accelerator is pushed it pulls more fuel. The stft gets into -10 to -15 through 1100-2500 rpm. The stft doesn't go positive at all during idle. I tested and pulled a vacuum line at idle and that's the only time went lean (positive).The ltft stayed at 0.0 but I was just idling for 10 mins, car from cold to fully warm. IAT reading was good. ETC sensor was good as well. (haven't driven the required miles from ecu reset for LTFT)

I'm not sure if that is normal for this vehicle. O2 voltage bounces from .500-.715v at idle. More towards the rich side?

Basically, when it's cold it will crank normally and start at about 2k rpm then will surge from 2k to 500rpm quite a bit and I have to catch it with the gas pedal or it dies. I rev it out to about 3k and after a second it catches itself and idles at 750+-and runs fine. Once warm I can shut it off and restart it with zero problems.

today it was about 60* outside and when I went to start it, it started and only surged once and caught itself. when it's colder it surges much more whenstarted to the point it dies. IF I just let it surge it will die. When I attempt to restart it, it turns over and dies immediately and I have to let it sit for a while before attempting again.

replaced:
maf sensor
ect sensor
air filter is good (doesn't seem to be any leaks after maf, haven't confirmed the injector seals though)

I think the O2 sensor is original and the car has 186k miles. Should I start with a new upstream o2?

O2S12 is .500-.790 volts fluctuating.
O2S11 is 2.250 volts

Idling after 25 min drive


EDIT:
Today I've driven well over the miles needed for LT FT to adjust and it never moves. It always stays at 0.0, I can see te ST FT moving, while cruising more towards the rich side with light throttle.

can a bad battery cause the surge upon starting because of not being able to provide the correct voltage to power injectors etc? I see it's being charged up to 14-14.3 while driving but immediately after I shut it off and the battery is tested the voltage is around 12.7, battery does look like it's leaking a little and about 7 years old?


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## VStar650CL (Nov 12, 2020)

Ordinarily I'd be inclined to think you have a leaky injector or a fuel pressure regulation problem with the STFT running that far lean. Usually they run a tad rich at idle (deliberately, to keep it smooth) and only go to the lean side when cruising. However, the A/F sensor (front O2) is showing lean (I think yours has the 2V type so anything above 2V is lean, below is rich. If it's the 1.5V type then it's running _really_ lean, but I'm pretty sure it's 2V). Anyway, that's weird since the ECM is correcting the STFT to the lean side. It should actually be correcting rich. So you may be right about the A/F sensor, it may be mis-indicating.

I very much doubt the battery could cause that sort of surging unless there was also a major problem with the alternator. That probably isn't the right tree to bark up.


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## Nissan0301 (11 mo ago)

Ok great. I was sitting there idling and it looked like the o2 wasn't bouncing around. Why would my long term fuel trims stay at 0.0? Slowed o2 response?

is there a way to tell if it's a 2v or 1.5v or do I have to remove it and is this the downstream sensor or upstream? The .1-1volt is the up stream one in the exhaust manifold right?

edit: on the drive I just did I noticed the LTFT actually moved a little, went to -3 then back to 0.0 but not much else after that.


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## VStar650CL (Nov 12, 2020)

Yep, the upstream is A/F, the downstream is a traditional O2. The upstream is actually used by the ECM for fuel trimming and has pretty much instant response. The downstream is strictly for the EPA, it only monitors the cat and has no other job. The ECM doesn't use it in running the engine. The "oscillations" you see in the rear O2 only mean anything when you're cruising with the cat lit, and the ECM is causing them deliberately by cycling the mixture rich-lean to watch how the cat responds. The sensor doesn't do that by itself. 

Give me a little while to pull up your FSM, I'll verify whether your A/F sensor is 1.5 or 2.


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## Nissan0301 (11 mo ago)

Thank you for your time and help. So on my live reader the o2 I should be looking at is o2s11 for info right? If so that one never goes above 1 volt and never under .1 but it does seem like it's getting sluggish when oscillating. Sorry if I'm confusing things up.


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## VStar650CL (Nov 12, 2020)

Yep, FSM says yours are 2V (actually 2.2V). So it's reading slightly lean but very slightly, I dunno if I'd call 0.05V enough to matter. That means it's running at stoichiometry with the lean STFT, so either it's getting a bit less air than the MAF indicates or the injectors are delivering a bit more fuel than the ECM's map calls for. Anything within 10% or so on STFT can be considered "normal" depending on operating conditions, so I'd say we need to find another tree to bark up. Next question is, have you ever cleaned the throttle body? How about the PCV valve, ever replace it?


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## Nissan0301 (11 mo ago)

Yeah my o2s11 goes lower when WOT and it's around 2.1-2.3 at idle. 

I have not cleaned the throttle body. I did clean the PCV or should I just not mess with and get a new one? Would a bad PCV cause that surge when cold by letting air slip past what's calculated by the MAF?

Basically everything on this car is original and was a family members who never really did maintenance so I'm stuck with it all starting to come due at once.


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## VStar650CL (Nov 12, 2020)

Nissan0301 said:


> Yeah my o2s11 goes lower when WOT and it's around 2.1-2.3 at idle.


If your scanner will graph and you watch it while doing a WOT followed by a drop-throttle, you'll see what looks almost like a spark-coil primary pattern, a big spike rich followed by a big spike lean, then leveling out again. That's normal stuff. Sudden acceleration needs fuel and sudden decel needs the injectors almost full closed to prevent backfiring.



Nissan0301 said:


> I have not cleaned the throttle body. I did clean the PCV or should I just not mess with and get a new one?


With those symptoms and readings, I'd say there's a real good chance the throttle plate is badly carboned. Pay the most attention to the back side and bottom edge, the best tool is a toothbrush. Don't force the plate open by hand, have an assistant push the accelerator to the floor with the key on and let the TB motor open the plate. I wouldn't screw around with the PCV, just replace it.


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## Nissan0301 (11 mo ago)

Alright, I'll start there soon and see what happens. Thanks again, once I do that I'll report back with hopefully good news.


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## Nissan0301 (11 mo ago)

Replaced PCV it didn't help with the original condition. I haven't cleaned the TB yet but will be doing that next. I did notice recently 2 times I had a pending code for p0340 (camshaft sensor) should I look it replacing this as well or test and remove it to overall check it's condition?


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## VStar650CL (Nov 12, 2020)

Nissan0301 said:


> I had a pending code for p0340 (camshaft sensor) should I look it replacing this as well or test and remove it to overall check it's condition?


Check the wiring to the sensor, but if you don't find issues, replace it. There's no reason for a CMP to ever miss teeth, and there are no "rationality" DTC's for the crank and cam like there are for MAF's and some other things. So P0340 basically means the ECM saw the CMP go flatline at least once. Missing a tooth here and there won't cause a code but will cause goofy engine behavior, and since reluctance-based signals gain strength as engine speed rises, intermittency in a dying sensor will usually happen at idle and cranking speeds. So I'd say you can treat the pending P0340 like a canary in a coal mine. It could be causing your whole issue.


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## Nissan0301 (11 mo ago)

Alright, will do. I have a sensor that will be arriving in a week or so. Thank you. I'm just trying to get to the bottom of this to hopefully help someone else in the future.

A quick question, how long should the car be in open loop after starting? Mine is in closed loop immediately after starting it per the live data.

Edit:
Car failed to start multiple times this morning, popped the hood and unplugged the camshaft sensor. With a little feather of the gas pedal it started and idled without that weird surging.


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## Nissan0301 (11 mo ago)

Tested it again, started the car again after sitting for 6 hours until completely cold with camshaft sensor unplugged, this time there was no check engine and it started and idled completely normal, like it always has. 

It has horrendous power feeling, extremely sluggish with the sensor plugged in. Hoping that new camshaft sensor finishes this saga.


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## VStar650CL (Nov 12, 2020)

I'd say that's a smoking gun, that sensor is working but missing teeth. If it was flatlined, taking it loose wouldn't change anything. Most Nissans will start and run with a dead cam or crank sensor, but it takes a long crank before the ECM gives up and says, "Okay, that sensor doesn't work." On 6's and 8's you generally need to disconnect both cams if one is bad, that's a case of Hitachi being weird with the ECM software.


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## Nissan0301 (11 mo ago)

VStar650CL said:


> I'd say that's a smoking gun, that sensor is working but missing teeth. If it was flatlined, taking it loose wouldn't change anything. Most Nissans will start and run with a dead cam or crank sensor, but it takes a long crank before the ECM gives up and says, "Okay, that sensor doesn't work." On 6's and 8's you generally need to disconnect both cams if one is bad, that's a case of Hitachi being weird with the ECM software.


Thank you, I appreciate your time in helping with this issue. It's been a pain but glad it should be done for now.


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## VStar650CL (Nov 12, 2020)

Happy to help, and once it's fixed, happy motoring!


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## Nissan0301 (11 mo ago)

Just wanted to finalize this. I replaced the camshaft sensor with an aftermarket one (OEM one is being shipped and arrives soon) and the car instantly started up, much better power and much better gas mileage.

Hopefully this thread can help someone else in the future.


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## VStar650CL (Nov 12, 2020)




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