what is the problem? How will cost to repair it?

Well there are two things here, first you need to replace your timing belt and get the car timed and I would do it soon before something happens to the engine. The second thing is to have the trouble code read on your car to see if there are any other codes and problems that need to be fixed.

There is no timing belt but a timing chain in your car, so the warning represent something else. You need to get your car to a BMW specialty shop or to the dealer to get a computer diagnostic. I assume you do the maintenance services regularly and the spark plugs where replaced at 100K miles. There might be a mass air flow sensor, cam and/or crank sensor, throttle body problem, slugged up VANOS (VVT) assembly, etc... Anyway, you need to get it diagnosed. Zee

I had the same problem. It started about a year after I bought it brand new. They changed the thermostat. It helped but would stall in cold weather. Now 10 years old & had to have replaced again. Scary, it would stall when I was pulling out into traffic. Could be a lethal problem. I asked the dealership if there were any recalls, no, I don't think they have a national database or whatever. Hope no one gets killed.