My '86 300SDL W126 OM603 has very low vacuum when starting up cold. It will only pull about 5" vacuum, even with all vacuum hoses plugged (except for the brake booster). Vacuum will go up when throttle increased, but back to about 5" at idle. After running for some minutes, will go up and pull around 21" vacuum all day long.

Is this a sign of a failing vacuum pump? Thanks

same thing happened on my 617. i replaced the check valve, cleaned out all the vacuum lines, etc. nothing. had to put in a new pump and that fixed it.

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1981 NA 300D 310k miles

I have the same problem with my 190d, same pump model. The only inconvenience is it will not turn off shortly after start up. If you can put up with the inconvenience then do nothing. I replaced it.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Hmm, my 190d does this too. I haven't gone through the vacuum system to check it out, but hearing this is an issue with others makes me wonder if I should look into a new pump, considering what can happen if the bearings decide to jump onto the timing chain. Can anyone add insight into a potential cause for this?

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1963 Ford Falcon Convertible
1972 220D 4-speed
1986 190D 2.5 5-speed
1999 300D