It's just recently got really cold here (~5degC and under), and sometimes (not always) when I start my car, it idles very unhappily for a few seconds. The revs rise and fall and the engine sounds like it might stall. If I press the gas while it's doing this, there's a delayed response before the engine revs a bit -- but not as much as the pedal movement should call for.

It sorts itself out after about 15 seconds, and doesn't happen with a warm start. I'm sure there's no harm being done, but it sounds bad and makes me look like an uncaring lout. Who, after all, would allow a BMW to fall into such abject disrepair?

I think it's most likely a vacuum leak somewhere that only becomes a problem when the materials contract a lot in the especially cold weather.

Any thoughts?