These beasts (and as you know from having an S500 they are beasts) can have one thing go wrong that creates a domino effect. A tune up may help, but I don't think that it's going to solve your problem. Have you had a Benz go into "Limp home" mode before? It's not a "I think" it's definite. The pedal goes to the floor with no acceleration (your symptom) and the tranny will either stay in 2nd gear or jerks around trying to do something that the computer won't let it do. My mechanic told me that when a sensor goes bad the computer gets a strange signal and gets confused and tries to fix the problem. I might also suggest that if you are getting strange signals from the computer that you might have a bad wiring harness. It is renowned on these early W140s and can cause all kinds of strange electrical problems that don't make any sense. Good luck

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Old age and treachery will allways overcome youth and skill!

1993 S500
1984 380SL