Hi there, I recently purchased a 2002 Trailblazer LTZ 4WD. 4.2L inline six. 177,000 miles on it.
I've been doing some maintenance on it, it was leaking oil from the valve cover so I pulled off the intake manifold (you have to to get to the valve cover) and there is a lot of wet like oily grimy residue in the intake and the heads. What causes this? I haven't pulled the valve cover off yet, may do it tonight.
It was supposedly taken good care of by previous owner. was sitting last 2 years without being driven. but with plugs and coils, O2 sensors, fuel filter, etc. it runs really good.
however, it does have an evap problem. I found a leak and fixed it but still have code for evap leak. don't know if this would have anything to do with it. I plan to drop the tank soon to look into the leak.
Here'* a pic of head. intake was the same. cylinders all look similar. you can scrape this off like mud.
One last thing, I cleaned the intake, but is there a way to clean out the heads?
Thanks for your help!

More than likely from the PCV.

here is the valve train. doesn't look to bad.



valve cover

no PCV on this engine. it has a hose that goes from air cleaner to the valve cover. according to my FSM this supplies fresh to the crankcase. then there is a hose that goes from the lower part of the head to the intake manifold, this lets out crankcase vapors I think. nothings clogged. but could that be why I have the sludge in the intake? I can't imagine this being normal, maybe it is, there aren't any symptoms, car runs good. I just thought that was a lot of gunk.

What ever they call it that is Positive Crankcase Ventilation and it picks up oil vapor and it will condense on various areas of the intake. This is normal.

carfixer007 thanks for the info.
putting her back together today.

I'd say cleaning the ports out might cause more harm than it solves. Even if you're meticulous with a vacuum some chunks will fall in and might create issues. If you never took it apart you'd never know the difference.