Hello! I'm new to this so I hope that I'm following the proper steps for trying to get my issue resolved. I need the help of this community to try and diagnose a pesky problem...

I have a rare 2011 G37S Sedan 6MT that has a check engine light problem. When it first went off last year, the diagnosis was:

Diagnostic Trouble Code P0300

• Random/Multiple Cylinder Misfire Detected

My dealer said that you have to replace ALL SIX engine coils and the problem will be fixed...And it worked...Until 2 days ago when it popped up again with the same code.

76,000 miles...Perhaps new plugs would do the trick? When the light is on, the resting RPM is at 1000 instead of the normal 500. And of course, I was on the way to my mechanic today for him to take a look and the light went off and the idle was back to normal. The last tidbit of info for the puzzle is the occassional burning smell from under the hood...It does not happen often but when it does, I wonder if it is something linked to the issue.

Any ideas that anyone could offer would be great.

Thank you,

Rob

 

I would replace the plugs because they're cheap and probably need it is the coil pack was bad and it fouled a plug or two or six.

 

Thanks - I will eventually do it - The light stayed on 3 days and then shut off - Another interesting tidbit is that when my Allstate Drivewise device detected the check engine light last year, it was designated as an urgent repair - This past go-around, it said that it might not need attention

 

I want to thank all of the people for commenting and contributing to the this thread...So after a week at the dealership and a 300-dollar diagnostic fee, I found out that the check engine light / P0300 code was not for the new coils that I installed or the new plugs that I installed...It is for a fuel injection problem...The dealer wants $2300 to replace the fuel injectors...Friends are telling me to use STP or Techron Fuel Injector Cleaner first...I bought 4 cans and have the first one in the tank now...If it doesn't work, what's next? A fuel injection cleaning from a mechanic? Let me know what you all think...Thank you

 

P0300 code means the engine is randomly misfiring and it cannot pick a specific cylinder thats causing it. I strongly doubt all your injectors are bad, verify with the dealership paperwork that they tested for fuel pressure, ask what other diagnostic steps were performed, etc.

 

Just rip all the injectors out and fuel rails get gtr injectors new fuel rails and new fuel pump and run e85 and be done with it 😂. Ever tried seafoam to clean fuel system?? Pour half the can inside another container like a measuring cup and pull break booster vacumme house off and let it suck in a little bit at a time so it doesn't flood then take other half of the can pour into gas tank, then hop in car give it a few revs up to about 6500 rpm "its gonna smoke like a bitch cause you are burning all the carbon off the pistons and **** all through the fuel system" take it down the road and get on it 1st-4th so you blow all the crap out the tail pipe that should clean it pretty good injectors and all. I've done it to my 03 coupe with 115 thousand miles twice in the past 20,000 miles, you'll be amazed how much crap it blows out.

 

Seafoam in the intake is great for cleaning the intake and valves but won't do anything for cleaning the fuel system and injectors.

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Thanks for the input. The dealer was sketchy only saying that all 6 injectors needed to be replaced and it was $2300. They were not surprised when I said NO. They had the car for a week...The 6 coils and 6 plugs are new...The wiring is fine...I'm on my second bottle of STP Fuel Injector Cleaner...If the check engine light doesn't go off in the next few weeks, what do you recommend? The resting idle with the light on is still at 1000 instead of the normal 600...And there is a faint burning smell coming from under the hood. The car appears to be running OK and the combined mileage is still 19mpg which is where it has always been.

 

That's why half the can goes into gas tank other half you put through vacumme hose to clean "intake and valves".

 

The light went off when I went out to lunch today...The resting idle is back to 600 RPM...Let's hope that it's fixed...Thanks

 

Sounds like you got a bad batch of gas that had more trash in it than usual and it's possible it clogged the flow/spray on the injector itself. I'd run 1 more bottle of stp injector cleaner on a full tank of BP 93 and if it doesn't come back I'd say that was the issue.

 

I would keep an OBD2 scanner handy in case it throws the CEL again, you should always scan when it pops up even if you know what code it's thrown lately. Never know when a second (third, fourth, etc) code is going to pop up that will help narrow down what the actual problem is.

Burning smell under the hood is definitely bad, you need to find out what's cooking. Could be electrical, could have a fluid leak, etc.