[fullofquestions]

The short version is:
1. how can properly test the Bosch 0221504470 ignition coils? I replaced one coil and everything worked for a week. But now I'm getting P0300, P0304 and P0306. So I'm leaning towards replacing the remaining 5 coils and would like to test the old ones so that I could keep the ones that are working just in case.
2. Given my description below, how would you go about troubleshooting these codes on this model car? Any pointers is much appreciated because it seems that for other cars there are a bunch of items to check. I would like to know if there are a certain set of steps that may be more applicable to my car.



Here is the longer version:
I realize that this probably requires that an expert have a look at the car though I would like to take this opportunity to learn more about my car. It is a 2007 328i SULEV (E90 N51). This is what happened and what I've done:
* FYI: car had the valve cover gasket replaced in May of 2015 and the car worked fine afterward
* in early December the car started to idle rough and I checked the obdii, code was a P0302
* I switched coil 1 with coil 2 and after driving about 25 miles the obdii code was P0301 (so I thought that the coil originally in cylinder 2 was faulty)
* I bought a new coil (Bosch 0221504470/0044). I replaced it into cyclinder 2 and the car worked fine for about a week. (attached is a photo of the coils. The top coil is the new one.
https://drive.google.com/open?id=0Bz...GxWb09ZN05GMk0
* After a week the car started to idle rough, like before. The new obdii code was P0306
* So I went ahead and bought and replaced all of the spark plugs with Bosch FR7NPP332
* After replacing the spark plugs I have the same idle. Note that when I start up the car I definitely smell nasty exhaust. Attached is a photo of the old spark plugs labeled by cylinder. Notice how the spark plug from the second cylinder has a ring of burn brown debris on the ceramic.
https://drive.google.com/open?id=0Bz...XNTdzVxQWxDMjA
* Current obdii status
Stored: P0306
Pending: P0306, P0302, P0300, P0304
* I've tried to check the old spark plug resistances but I'm getting pretty much 0. Also, I'm measuring the resistance of the new coil (bottom two pins) and I'm getting something very low in the order of 2 or 3 ohms which I think is correct. The point of all this was to try and see if the spark plugs can give me some sort of guidance. I also want to keep the coils that are still good.

Lastly, I see that there are many things that can be checked at this point such as: vacuum hoses, MAF, fuel filter, even the distributor?
Does anyone have any suggestions on what I can reasonably have a look at before taking the car into the mechanic? I've heard that when you replace a coil sometimes the other older coils also go out so it solves the issue to replace all of the coils (http://www.bimmerfest.com/forums/sho...d.php?t=755644).
Note in the image below how coil 5 or 6 has lost part of the plastic cover. Is that necessarily an issue:
https://drive.google.com/open?id=0Bz...mVPNzdJLXhYVjA
If that is the case is there any sort of check that I can do on the old coils? I would like to keep the old coils that are still working.

Whatever clear steps that you may have are much appreciated.

Testing Coils
http://www.aa1car.com/library/ignition_coils.htm