I searched but maybe this is too basic.
I am planning to systematically replace my vacuum lines, connectors and fittings. I have no problems now and hope to avoid them.
Since the car (89 300CE) constantly holds a vacuum, when I break into the system to replace a line, the vacuum is lost. Will it re-establish the vacuum when I re-start the car after the replacement? Do you "pinch off" vacuum lines like a fuel or coolant line to isolate the spot you are working on?
Will I need the vacuum testing tool? Which one?
I can't find a schematic of the vacuum system comparable to a wiring diagram. Do I have to buy the CD?
thanks

Will it re-establish the vacuum when I re-start the car after the replacement? - yes

Do you "pinch off" vacuum lines like a fuel or coolant line to isolate the spot you are working on? - no just disconnect it and use a MightyVac to test that circuit. You will need a MightyVac.

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Jim

Replace one line at a time ( with the engine off ).
Your vacuum will be restored, the minute you start the engine.

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2007 C 230 Sport.

I to was also thinking of replacing all my vacuum lines one at a time,, I was told that even a slight leak would causemy car to idle improperly. Does anyone have a schematic of the vacuum system on a 1991 300E?? What is a Mighty Vac and how will it be used??

I have no problems now and hope to avoid them.
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Reminds me of the saying....."if it ain't broke, don't fix it".

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1986 560 SEL (159K miles)

Understood, but with the age of the vacuum lines and connectors, they are going to and in some cases already have started to get brittle and oxidise if you will..... i just want to do it piece by piece ,, a new vacuum line and connector will not hurt or adversly affect the engine in my opinion,,, now if its something like an alternator or something like that i always say if it isnt broke dont fix it..

I agree Rockman59, but from what I've read here, a vacuum line failure can strand you. Mine are getting brittle.
But mostly I can't resist messing around with my car. So my answer starts with, "An ounce of prevention...."