My 1989, 560SL was garaged for couple of years. Battery was dead. I jumped started it with difficulty. Took an hour to start it. It started with hesitation and missing with the engine light on. The next day I took it on the freeway. It ran great. Since then it has been running perfect. The only problem is the engine light which is always on. Anybody has any idea why? I would really appreciate your help. Thanks.