Intermittent Misfire
 

My Mini has a problem, and I don't know how to narrow it down. I'm driving an 08 Cooper S JCW package. I've owned it for about a year and a half, and she has ~60k miles. I don't know how much of a difference the JCW package makes here, but figured I'd mention it. I'm getting an intermittent misfire issue, and a sound/mechanical issue. The codes indicate that the misfire is not with a specific cylinder, and suggest that it could be anything from an ignition issue to a vacuum issue. There are no codes for anything other than the misfire. I have recently changed the plugs and cables with manufacturer recommended.

The problem might actually be two problems, but I'm not sure. When I start the car, and this does not happen every time I start it, I get two things happening. First there is a rattle, like an old, noisy diesel starting. Then the engine diesels like it is a big V8 with a crack in the distributor. The RPMs repeatedly drops below 500, and if I press the accelerator the RPMs drop before going up. That alone says vacuum leak to me. If I actually get on the road at all the rattle continues, but invariably stops abruptly within 5 minutes after the motor warms up a bit, and the car drives like normal, and the CEL goes away. On some occasions the rattle stops and the car drives like normal, but there is no turbo boost.

My problem is that I am not close enough to a shop that can look at it, or even listen to it, before the problem stops. In addition, my situation with transportation is such that I cannot leave it at a mechanic overnight in hopes that it will act up for the mechanic. I fear that this is the beginning of a head gasket problem, a turbo problem, or a timing belt problem. If anyone has had similar a experience, I would appreciate any input.