My 95 c280. Stays in open loop at all times. The fuel trim is stuck on -7.5. I need help figuring this one out. The car runs great, with one exception. On start up, it idles high at first (normal). Then drops to 1100, the stumbles almost to a stall. When it recovers, its fine, with a slightly high idle. Its a one time stumble, but happens everytime I start it....hot or cold. This I can live with, but the Open loop,and no fuel trim concerns me greatly. I have found no posts addressing this. Any help would be grand. I do have a scanner, and can read data. It will not read o2 sensors. Side note: rpms drop to 700 when I remove oil filler cap.