My 190D would not shut off ( within the first 1 or 2 minutes ) when first started in the morning and the brake is weak. After a few minutes of driving then everything is OK. Search the database here and was told to measure the vacuum when car is first started.

1) Hook up a Mityvac and T the line to the brake booster. It measures 5 in when the car first start up.
2) Rev the engine and it creeps up slowly to 10, 15, 20 and then settled at 25 after 1 or 2 minutes revving.
3) Vacuum holds after car is shut off.

What is the problem here? A weak vacuum pump or that is the way it is for 190D.

Any info is appreciated.

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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.

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It should build up within a few seconds of start up. The main vac line goes from the vac pump to the brake booster. So at this point you could have a faulty pump or a faulty booster. Remove the vac line from the booster and plug the end of it. Then start the car read you vac again. If the gauge goes up to 25 in a couple seconds then your booster is leaking. If the situation doesn't change then the pump it bad. I'm not experienced with the 190's but the 123 chassis pump are rebuildable, so I would assume that yours is as well. But someone else can say for sure.

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I'm responding to this old thread as per your request earlier today in a different thread... thanks for linking me to this one; I figured I'd answer here in an effort to keep each of the threads on topic.

The behaviour you describe is definitely not correct; there's a problem somewhere for sure.

I've never measured the exact time it takes for the vacuum to build, but on my car it is possible to shut the engine off immediately after startup if you want, and the vacuum brake boost works immediately as well. If there is a delay in building up vacuum, it's a few seconds or less.

On your car, since the vacuum holds after the car is shut off, it doesn't sound like you have a leak. Since both the brake booster and the vacuum shut-off on the IP don't work on start-up, it seems more like a general vacuum issue than a specific faulty component (i.e. it's unlikely that the shutoff valve and booster are both independently faulty in the exact same way). So, I guess the pump would be the next logical suspect. I'm not an expert though so don't take my opinion too seriously!

In consideration of what can happen when the vacuum pump fails, if you have an original vacuum pump with exposed bearings, then you might want to change it out anyway...

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