Take off the hose on the other valve cover (other side of engine) and check down in the hole that the small end of the hose came off of. There is a very small hole in the bottom of that hole which is the "PCV" (Positive Crankcase Ventilation). Make sure this small hole is clean. You should feel vacumn on this hole with the engine running. If not clean it again. I had to run a drill bit of the same size in mine (84 500SEL) to clean it out. Fixed the problem you are having.

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84 500 SEL (307,xxx miles)