Thanks for the replies. All reinforced the conclusion I had reached preliminarily--that the shutoff gizmo was the culprit despite my being able to shut it off with the bypass line.

I am well aware of the possible problems installing the actuator; that is, the runaway engine. I have read the other threads' discussion this issue, and I knew about it from before. I once did the job on a 240D and had been warned then too. I prepared myself to react immediately should that happen.

On the 240D the failure was different: the diaphragm leaked oil into the lines. Rather it tried to but I had a clear fuel filter in the line to protect against oil intrusion. Many years back there was an article by the late Frank King in the Star magazine about the benfits of installing these filters in the vacuum lines. I did so and, coincidentally, two weeks later engine oil showed up in the one serving the shutoff gizmo. It had failed, leaking oil. Then a month later the main vacuum pump itself failed and leaked oil. The second filter I had installed in the lines intercepted that. And because the filter is clear plastic, I could see it immediately. I was very fortunate. Oil did not get into the vacuum line system which would have been extremely destructive. I cannot recommend those filters more highly.

My problem this time is that (a) there is no oil leak and (b) I could get the actuator to work doing the bypass. That is was made me pause, take stock, and ask for help analyzing. Many thanks.

__________________
Douglas
1959 M-B 220S cabriolet