X5 4.8is Shaking on cold start?

[vierpunktachtis]

I'm having some issues with my X5 that is really starting to worry me.

I bought my X5 4.8is in February, and here in Sweden we have pretty cold weather during the winter, and it's now starting to get below 0 degrees celsius.

About two weeks after the purchase of the car, the whole car started shaking really bad during a coldstart one morning. No enginelights were lit or anything, just shaking like it misfired or something. Got even worse when i tried to put a gear in. I then turned the car off and back on, and voilá, no shaking at all.

After that incident, i went to a local mechanic who read the codes and it had gotten 2 errorcodes (misfire on cyl. 6 and 8). So i decided to change the two cylinders coils and also changed all the sparkplugs to new Bosch original plugs. After that, i've been driving without any problems for about 8 months and 20000km.

So yesterday the problem came back again as i was starting the car after a frosty night. Did the same thing again, i turned it off and then started it again. Worked this time also. I have not yet read the errorcodes, but i'm pretty sure it's the same thing again because of the symptoms.

There has to be a reason for this to be happening. I really don't think the change of the coils were neccessary to begin with. I do know my battery isn't that good, but it has always started without any problems. Could the battery have anything to do with it? It's a OEM battery, probably as old as the car (2005).

Any idea of what it could be? It's really freaking me out!