280sl erratic cruise control

[oldan]

with cruise on the car surges forward and then backs off
it will do this continuously

Any thoughts?

Thanks

[oldan]

I guess I should have said the car is 1985.

Does anyone know if this is vacuum cruise control

[Diseasel300]

I'm surprised that you haven't received a reply since November!

Being 1985, you have the electronic servo system. You could have a fault in the cruise control amplifier, or in the electric servo attached to the accelerator linkage. Both are common.

Look at Kris Rose's website (he goes by JamesDean on this forum):
Overview — Cruise Control Repair

FWIW, my 560SEL was surging, essentially full throttle or nothing, very rough! Mine was the servo that was the problem. Fortunately I had a spare in my parts collection that solved the issue.

[oldan]

The car magically healed itself. Must be the German engineering magic.