I just bought my first BMW - used - in May of this year. I've been having this problem with the RPM's dropping 200-300 RPMs at idle. At first I thought it had to do with the compressor kicking in - to test this I ran it with/ without AC on. No real correlation. I have had it happen almost constantly on a daily basis, while at other times it runs smooth without hiccuping at all. It gives a very strong "bump", as if the engine wants to jump in a gear... Passengers feel it too and question me and I have no answer for it. I had the car checked by an independent BMW mechanic - he only works on BMW and was a master mechanic at the dealer I bought the car from for 8 years prior to starting his own business. I hadn't noticed this "" RPM bump" then - I had just bought it. The car seems to run fine once it gets moving - smooth and quiet, even when driven all day on a 300 plus mile trip - in fact, it ran the smoothest idle that whole day - it never did it at all. I'm wondering what to make of that - but it's intermittant excepting that one day and shorter trips ( 100-200 miles have also had the " idle bump"' Any idea what could be happenning? All systems say "ok" on the Nav screen under Vehicle info and other than this, the car seems flawless after I replaced the rotors and brake pads. I love the car - most fun I've had driving 42 years - should I be worried though and get it checked even though in all other respects, it seems fine?