Originally Posted by youngdoc1
Similar issue on my N52 128i. RPMs would dip below 6000 intermittently while stopped at a stop light, having the AC on would solve this issue somewhat. Brought it in to dealer, they found no faults but "adjusted idle values" which increased the idle RPM to around 7250-7500 about 2 months ago. No issues since, engine is smooth as silk.
Lol, you added to many zero's there buddy because if your car idles at 7000+ RPM that would be crazy loud and your car would be out of gas in no time.
To the OP, mines never went below 600 RPM and I have a 328i. But just make sure your new spark plugs are tightened/torqued properly and see if there is any difference. Also about the vibration try to see if your motor mounts are leaking any fluids.