I have a 1989 750il with about 90,000 miles and it's been having an issue lately. Intermittently the check engine light will come on and it then begins to run on only half of the 12 cylinders. This will go on for a while, the light goes out and full power is restored. One other thing that happens even less is that it won't start and it sounds like it's running out of sync.

Does anyone have an idea where I should start looking?

Thanks...Lee Griffin