[Benfoster15]

Im having trouble figuring out what is causing my misfires. The misfires only happen when the car has sat overnight or a long time without running. The misfires go for about a minute and then stop. After they stop i have no problems with the car but i need to solve this problem soon.

[arkie6]

Fuel injectors leaking are a fairly common cause for that. What is the index number of the injectors you currently have installed? The most current index # is 12. You can also pull your spark plugs immediately after a cold start and look at the porcelain over the center electrode. If they are black and wet, that is a good indication the injectors are leaking when the engine is shut down.

[Bimmer_Engineer]

So you should pull the plugs after the rough start? I’ve been having a similar issue...only last about 10 seconds though...and only after the car has sat overnight. I pulled my plugs this morning before starting the car and they were dry...the #1 was a little sootier than the others...

[AandSC]

Had the same problem. Knew I had good plugs, swapped coils, which left just the injector (assuming your code points to a single cylinder misfiring). Put a new injector in and resolved that issue.

[IllSic_Design]

Originally Posted by Bimmer_Engineer

So you should pull the plugs after the rough start? I’ve been having a similar issue...only last about 10 seconds though...and only after the car has sat overnight. I pulled my plugs this morning before starting the car and they were dry...the #1 was a little sootier than the others...

You check them after letting it sit over night but before starting it. If the injector(s) are bad then the plug(s) will be wet with gas from the injector not holding pressure and leaking gas into the cylinder.

[Bimmer_Engineer]

Okay that’s what I thought...I checked before starting and the plugs were dry...

[Benfoster15]

Originally Posted by arkie6

Fuel injectors leaking are a fairly common cause for that. What is the index number of the injectors you currently have installed? The most current index # is 12. You can also pull your spark plugs immediately after a cold start and look at the porcelain over the center electrode. If they are black and wet, that is a good indication the injectors are leaking when the engine is shut down.

Thank you! The injectors are stock so im debating wether i should replace the two injectors or all of them

[Bimmer_Engineer]

Here's some pics of my plugs...these have about 2k miles on them. Like I mentioned previously...the car is behaving similar to what the OP described, but the rough idle doesn't last as long...like maybe 10 seconds on an overnight cold start. These plugs were pulled after sitting 2 days...not wet at all. Plug #1 was sootier than the others. Any thoughts? I was thinking injectors before I pulled the plugs but now I'm not so sure...

[arkie6]

Originally Posted by Bimmer_Engineer

Here's some pics of my plugs...these have about 2k miles on them. Like I mentioned previously...the car is behaving similar to what the OP described, but the rough idle doesn't last as long...like maybe 10 seconds on an overnight cold start. These plugs were pulled after sitting 2 days...not wet at all. Plug #1 was sootier than the others. Any thoughts? I was thinking injectors before I pulled the plugs but now I'm not so sure...

Your plugs look fine. The part that is important is the porcelain insulator around the center electrode. If the engine is running rich, i.e. due to a leaking fuel injector, or burning excessive oil, that insulator will be black. Yours appear to be white / light tan which indicates those plugs are seeing the right amount of fuel.

With respect to pulling the plugs after sitting 2 days and looking to see if they are wet. The fuel injector and spark plug is at the top of the combustion chamber. If you have a leaking fuel injector, it will bleed off the ~700 psi fuel rail pressure into the cylinder upon shutdown. This would be a small volume of fuel, probably an ounce or two at most. I guess it is possible that the fuel would run sideways over to the spark plug and wet it on the way down, but I find this unlikely. And even more unlikely that you would see any evidence of the plug being wet after 2 days. How is the fuel getting on the plug at the top of the combustion chamber? On the other hand, if there is a small amount of fuel pooled on top of your piston due to a leaking fuel injector, the entire combustion chamber will be wetted by the fuel the first time that piston comes up during the first firing cycle. Excessive fuel in the combustion chamber will prevent that cylinder from firing. If you immediately shutdown the engine during a stumbling cold start and remove and inspect the spark plugs, you will be able to confirm or refute excessive fuel is causing the misfire by the plug tip being wet or dry and be able to point to which cylinder is the source of the excessive fuel if it exists. I would have your tools ready and the engine cover removed before attempting this test so as to not delay getting the plugs removed.