Your Positive Crankcase Ventilation (PCV) valve is blowing sludge from inside your valve cover. It IS supposed to vent into the intake - but it might be blowing sludge buildup. Time to pop open the valve cover and see what is happening.
If there is sludge, I would carefully remove it (no water or solvents!) by hand then do an oil change without adding ANY cleaning additives!
Additives can loosen up the engine to the point where you'll lose all compression (all the goo is washed out). With all the goo that might be holding your engine together missing, you might dramatically speed up wear in the piston/cylinder area.
Oh, and sludge is sometimes formed when water is mixed with oil - by a coolant system leak or by "frisky" driving in water...
It may be time for a rebuild.
I had a 64 Chevy with a straight six in college that was packed with goo under the valve cover. After a bit of cleaning, I decided to switch from non-detergent oil to detergent oil (nowadays, you can't do that - and for good reason!). Within a couple of hundred miles, the engine loosened up to the point where the compression was so bad that it wouldn't run anymore! It's not fun to try to get a college education and keep a POS car running at the same time!
Natually, this being the Internet, I may be FOS.
Any other comments?