Intermittent Engine Misfire with codes P0300 P0303 P0305
 

Hi guys,

2012 370Z Touring 163k miles

I've been dealing with an intermittent misfire since last fall. It has always occurred on either cylinder 5 or cylinders 3 and 5 plus the random misfire code P0300.

I first got a solid check engine light where the idle speed changed to 1000rpm until I erased the codes (this happened twice last fall, then it seemed fine).

The other day on the highway the check engine light was BLINKING on and off in sets of 5 and then eventually just went away and was fine. No solid check engine light after and I didn't clear any codes.

Took it to the shop and they scanned it and said there were no codes (no solid check engine light was on at this time).

Today it blinked again on the highway then went away after blinking like 2 sets of 3 times each.

Now codes were gone until I got a solid check engine light about a half hour later with codes P0300 P0303 and PO305. Same two cylinders.

Car mostly drives fine and I haven't noticed a misfire at all. The only other symptoms I can think of are:

-Sometimes engine seems to "skip" at idle like a small cough here and there
-When on the accelerator just enough to coast / using cruise control it seems to alternate between power on and power off kind of like the engine is stuttering / coming in and out several times per second.

Any ideas what this could be? Obviously I'm going to try to bring it back to the shop since they should be able to scan the codes now, but what do these symptoms suggest?

The issue started after the car had sat for 3-4 months without being driven much, but I've filled the tank 1.5 times since then over the last few months.

Could be a fueling issue (not necessarily the fuel itself). I would check the plugs firstly since your experiencing misfires on more than 1 cylinder. Maybe have the shop take a look at it if all plugs are in good shape.

I’ve had some strange intermittent issues like this on my g35 and it turned out to be bad coil packs. Sometimes they’d be fine, sometimes the car would misfire terribly. Since the car sat for a while, you could have gunked up injectors.

As a cheap first check, I’d throw in some new spark plugs and a bottle of redline fuel system cleaner in the tank with high quality 93 octane fuel. Redline is one of the best types that ‘might’ actually do something unlike most of the snake oil products out there.

If the issue persists, you may have to start replacing coil packs, but they’re only $50 on rock auto. Not terribly expensive…


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If the intake manifold (MAF & TB too) has oil in it (I’m sure it does) all that needs to be cleaned and catch cans added.

Oil causes random mis-fires, detonation, dead plugs etc..and this engine has serious issues with oil ending up in the intake system.

Also,

I have 6 good OEM Nissan coils (16k miles on em) id sell for $200 shipped if needed.

I quite literally had similar issue a month ago. Cylinder 5 misfire and random misfire.

I put new plugs in and no change. Decided to swap #5 coil pack to #3, lo and behold it shifted to cylinder #3.

Got a lightly used coil pack and plopped it in. Probably solved.

I started with plugs and coil packs. I ordered oem plugs and z1 coil packs off of their website and had my mechanic throw them on for me.

Wouldn't you know, the spark plugs were "the worst he's ever seen."

I bought and installed supposedly OEM spark plugs from ebay about 5 years and 50k miles ago but I remember them being suspiciously cheap at the time...hmm

Car is running noticeably better and the dash light hasn't come back so far!

Thank you everyone for the help / advice! I'm hoping this solves it. I did some fuel system cleaner as well while I was thinking of it.

Always best to purchase from reputable sources especially if it seems like a really good deal.

I got some knock off spark plugs off eBay a few years ago when I was more naive lol

I stick to rockauto for most parts now. Best prices by far


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I've got a similar horror story of purchasing "authentic" NGK Iridiums for my 08 TL that turned out to be duds about a year later down the road. Caused all kinds of misfires and the car ran like absolute crap. After investing too much $$ into coil packs from different brands (oem,NGK,Import Direct)that remedied the problem temporarily. I smartened up and pulled the plugs I had replaced only 12 months prior and Wallah !!! they were worn to nubs and black as soot covered in carbon and unburnt gas. I think running like this for an extended period of time played a role in my rings failing at or around 212,000m killed my motor prematurely (for a Honda at least). I'm still saddened by it till this day but you live and you learn :wtf2::stirthepot: