My 88 560SEL runs fine under normal acceleration. Everything is smooth right up to 100+. However, if I put the pedal to the floor, the car practically bucks like a horse almost like a severely clogged fuel filter. Accept, of course, a clogged fuel filter wouldn't just act up under those circumstances. If I back off the pedal a little, the shaking stops and accelerates normally.

It doesn't do this under any other circumstance.

Anyone else experienced this? A problem with the passing gear, perhaps?

Bill

Have you checked the tranny fluid? When was the last time the transmission fluid and filter were changed?

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1989 420 SEL

Sounds like an engine performance problem, check for codes. If you have none I would first change the, yes fuel filter, then check fuel pressure and move on from there.