Team,
2010 Maxima 3.5L, 164K. I have been having P0300, P0303, an P0306 for a few weeks now while troubleshooting. I have replaced all spark plugs, ignition coils, valve covers, gaskets and such as well as PCV valve. Codes came back and rough idle immediately with ignition replacements. After PCV valve, engine ran smoother, not normal for it, but better for about a day and then back to fairly rough idle and misfires starting at about 2500-3000RPM. Next is checking injectors (initially with long screwdriver technique) and reading O2 sensor data with a Zurich ZR13S. Easter egging my troubleshooting is not desired but I am hopefully there are some great minds on this forum to assist in ideas beyond just fixing one (expensive) component at a time. Thank you in advance for any assistance!!

 

Random thought but have you tried disconnecting the battery for an hour to let the PCM go to sleep and see if connecting the battery up after and running it does anything? I don't know about the radio lockout code headaches or whatever else can come up with newer cars when you disconnect the battery but if it wouldn't be messy its worth a try

If you have a scanner, have you looked at fuel trims and live feed data while its running poorly?

 

I just ran the scanner and got the following live data:
LAMBDA B1S1 1.00
LAMBDA B2S1 1.30
O2SB1S1 1.9V
O2SB2S1 3.0 V
MAF 0.4 lb/min
STFT B1 (about) 20%
LTFT B1 9.4%
STFT B2 25%
LTFT B2 9.4%

FUEL SYS 1 CL
FUEL SYS 2 CL

from this data, kinda looks like B2S1 may require replacement.
STFT B1 seemed off compared to the others.
MAF seemed kinda low. At idle, think it should be around higher.

Thoughts?

 

You can try cleaning your MAF sensor with MAF Sensor Cleaner. It made a noticeable difference for me.

 

​​​​​​1. What brand spark plugs and what brand ignition coils did you use?
2. Have you tried doing the pulling of ignition coil while running method to see if engine stumbles even more?

I'm curious if your wiring has any deterioration...

 

Cleaned the MAF (had previously but up for anything) but no changes to STFT. Using the carb cleaner fluid and a vacuum gage, shows indications of intake manifold leak (about 10” of vacuum vice 20-25).

Just finished breaking down engine to upper manifold removed and verified all areas that there is no obvious leaks. Gasket is good. Spark and coils all changed. PCV changed. All vacuum hoses changed. B2S1 (closest to radiator) changed. EGR is a potential as STFT still registering pegged high at 25%.

After vacuum hoses all changed, STFT B1S1 indicates more normal range. Concerned deeper issue with lower intake manifold gaskets but no other ideas.

 

Spark plugs from 1A Auto so TRQ, no indications that that is the issue though. No deterioration to cabling but the wrap had degraded significantly (expected age since over 14 years old). Nothing looks burnt or damaged.

 

You have a p303 and a p306. Those are misfire codes for cylinder 3 and cylinder 6. If that is not an indication that there's an issue there then I don't know what to say. First things to check are usually plugs, coils, and injectors which you've done two of those already although for some reason something makes me question the quality of the plugs and coils.
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I have never heard of TRQ sparkplugs but I sure wouldn't use anything than the OEM specified plugs which are Denso/NGK for Nissan.

Seeing that you used TRQ sparkplugs, I will assume that the next last question of what brand coils you use will be answered with a similar brand or aftermarket brand.

Not sure if you're new to the Nissan world or not but these cars are picky with the electronics and sensors that you install in them.

You didn't specify if you tried pulling the coils individually to rule out any difference in stumbles...

Lastly I'd do a smoke test to check for any crazy vac leaks that have gone undetected
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I had most of the symptoms when my right tail lamp housing filled with water. As others have mentioned, our gen are very picky about circuit integrity and voltage (especially ac ripple).

 

it was fuel injectors. Replaced all six but #6 was the culprit. Running like a champ again.