A friend of mine has been having the same problem as you. Yesterday was looking at a manual at another. Shop owner said check the {Alda} the diaphram may be tore. Have you checked it before pulling the pump. I will check with him tonight and see if it was bad.
These problems are almost as bad as vacume problems.
Good luck and thank you for all your post.
Charlie

You can test the ALDA with a MityVac that can produce pressure, like the Silverline Plus 4050 kit from thetoowarehouse.net (for ~$60 I think). It should hold pressure and bleed down slowly below 10psi, and hold pressure steady above 10psi. If it bleeds down fast (watch the needle swoop down) or won't hold any pressure, the shaft seal is bad. It's not hard to replace but good luck finding a Bosch shop who can identify and/or order the seal.

If the internal diaphragms rupture, they won't press down on the I/P shaft, which will cause a very rich condition with no boost (black smoke, low power). This is harder to test for. You need to remove the ALDA, press gently on the output shaft in the hole (with a small screwdriver or something), then apply pressure to the input port with the MityVac. The shaft should move upwards (into the ALDA body) as pressure increases. It's kind of hard to explain.

Photos of the ALDA internals are here:

http://www.meimann.com/images/mercedes/OM603_intake/



Regards,

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