Engine vibration and intermittent roughness
I recently cleaned the ICV valve. After I had reinstalled everything, it had turned out that the new hose clamps I had installed caused the intake control arm (I'm not sure the exact name of it, but it is what opens and closes the intake) to come loose. I figured it out and changed the angle. But anyways, after this I drove the car about 50 miles round trip. During the first portion of the drive, everything ran smooth. When I left to come home, I noticed the car had a very slight vibration. It wasn't there before (and since then I sat in another M3 and it definitely did not have it either, so I know its not in my head). Also, shortly after the engine started running rough. You felt it while idling and also while accelerating.
The next morning, the vibration was still there, but the roughness had gone. Now the roughness intermittently comes back. I am not sure what could cause this. Originally I thought one of the spark plugs might be fouled, due the car running rich for that little bit while the intake stayed closed. I took the plugs out and inspected them and they didn't look dirty. So now, I'm not sure what this could be.