Could be far too many things to mention, this is one of the few cars I have ever worked on that I knee jerk on hooking up to the diagnostics and pull codes so I would atleast have an idea of where to start. Its possible if you wrote a very long highly detailed description of starting and idling someone might be able to make a good educated guesse, or an experienced tech might be able to pin point it if they started it themselves. Please don't get me wrong, I love the 750's, there is something invigorating about v12's, but the techs at the dealer will hate you if you waltz in with it and you are likely to get the guy at the bottom of the foodchain working on it. So, either drive it by a dealer and pay for the quick check, or gives us loads of details.