Misfire, startup stuttering resolved itself?
 

A week and a half ago, I was experiencing some stuttering, a random engine stall, and SES light. The weather had been 20-30 degrees F that week and my gas tank was probably only 1/4 full. So after a few days of leaving the X5 on its own for fear of the dreaded oil separator or intermediate lever issues, I had borrowed an OBD code reader and got a misfire code (P0304 - Misfire in Cyl #4). No oil leaks or evidence of oil anywhere. To be sure, I had decided to run the car to see if the symptoms returned. I let it idle for a few minutes to warm up, and indeed it idled OK. SES was still lit but no stuttering even despite temps still being in the 20s. I decided to run some errands and let the car run for 30-60 minutes to help heat up the engine and perhaps expell any moisture in the OS, if it indeed had any in the first place. Ran fine throughout the drive. Fast forward a few more days. Weather warmed up only a hair above freezing, X5 starts ok, still no stuttering, idle OK, and this time the SES disappeared. X5's been running great ever since I put in a full tank of gas. I suspect that perhaps some old gas in the tank plus any residual moisture might have entered the fuel lines. I typically fill up once every month and a half which I'm sure people are wondering why I even have this SAV if I don't drive it.

So fears lead me to believe the worst, but all seems to be ok. While I can't completely rule out the OS or intermediate lever issues, I think for those experiencing similar problems with no evidence of oil leaks should hang in there and "wait n see". Might work itself out with no $$$$ out of your pocket. Knock on wood.

For reference, I have a 2004 4.4i N62 (6/04 build date) with about 38K miles.

I wouldn't worry. These electronical things have their misteries and it generally doesn't matter if they can be wrong sometimes... As an example, I replaced recently my cam sensors as a preventative maintenance. After having started the engine, the SES light went on, and the code concerned a "faulty intake cam sensor" and misfires on several cylinders. Began to wonder about replacing again this brand new sensor but I quickly noticed that the code didn't come again. I've done several hundreds of kilometers since, no problem, no light, no misfire anymore. It should probably be sufficient that there is an intermittent loose connection in the sensor connector (yes I cleaned it) or even the computer going temporarily south because of the new sensor to lighten up the SES once...

Of course, in your case (cold weather), getting a quick look to the spark plug #4 would be safe to seer if some oil has not find its way to this cylinder due to a OS problem or anything else. Just for safety.

I had the same issues you had and it also went away on its own with me... very odd...