Engine problems Omega 2.5 V6

Hello people. I’m desperate, my Omega 2,5 V6 Bj 98, Automatic, ran perfectly. When suddenly, from the way home, no real performance came. He ran only on 5 cylinders. I to BOSCH service in the neighborhood, allegedly ignition coil defective. Renewed, 326 euros incl. work. Picked up, and exactly as before. No performance!!! Now he is standing since 02.11. in the workshop, and they told me: We find no error. Computer, and engine tester say:No error! Ignition cable and K Everyone is all right. At the cold start, it runs great. As soon as it gets warm, a cylinder falls out. ( According to BOSCH service). Is now slowly no longer in the mood for comfort. Does any of you have an idea what that could be??? Thank you very much. Dirk