MatthewakaMatt

My car keeps giving the P0300 CEL code "Random - Multiple Misfire Detected" on cold starts on cold mornings. The car's a completely stock 2009 G37 MT sedan with 47.5k miles. The code only comes in within a minute of starting, and only on cold starts when the temperature is in the 30s or below. The car drives perfectly fine with no noticible signs of an actual misfire or other engine problems.

The first time the CEL came on it also had P0305 (#5 missfire) and C1109 (low batter voltage). The battery was on its way out, so I went ahead and replaced it. I have not gotten either of those codes again since then. In addition to the battery, I put in new air filters (were grimy but not horrible), and filled it up with a fresh tank of gas.

Some other threads mentioned this problem on cars with exhaust leaks from recent exhaust work. There weren't any obvious leaks I could see or feel, but I guess it still is possible there could be a small one.

Would spark plugs be the next thing to try? They seem like a default misfire culprit, but I'm less than half way through their normal replacement interval.

Landshark

maybe a bad coil pack ...

MatthewakaMatt

A coil pack is definitely a possibility. I just wish the codes would narrow it down to a specific cylinder. I don't really want to replace all 6, and then still have the problem persist.

VRedG37s

Had this issue on my 2010. Would randomly throw a code after the engine has started and sometimes you would feel a shake from the misfire. I replaced the battery in addition to cleaning the throttle bodies. I have not had any issues since then.

Most likely the throttle body flaps stick which affects the engine during cold starts as the rpm is higher.

Spark plugs don't need to be changes until 100,000+ miles as they are iridium tipped.

crookncastle

random misfires are not caused by a single ignition coil going bad. and i would not suspect all 6 ignition coils going bad all at one time, this is highly unlikely. may i ask what octane fuel u r using in your ride? these g's are engineered to run on 91octane so anything below that octane rating will cause inefficient combustion in the engine on top of the cold start condition which can result in a slight misfire especially during cold start ups.
next i would check you fuel pressure to make sure you its not a bad fuel pressure regulator or fuel pump issue.

MatthewakaMatt

I cleaned the throttle bodies tonight. They were moderately dirty, so it was good to clean them up.

I always use premium gas for this car (93 around here). A bad tank of gas was my first guess, but I have refueled a couple times since the issue started. If the CEL comes back again after cleaning the TBs, I'll start checking the fuel system next.

Thanks for the input!

Surfnazi

When is the last time you cleaned the maf sensor

esesnipey94

Im having tha same problem. Only on cold starts. Never while driving or warm starts. Car runs like a champ other than this. 8.4 1/8th mile at 85mph. So I know I'm not missfiring. I have to keep clearing the code because the characteristics of the idle are annoying while the code is active

MatthewakaMatt

Now that cold weather has returned to the east coast and my CEL hasn't, it looks like cleaning the throttle bodies fixed the CEL issue for me.

Thanks everybody!