I took off the upper intake and found a black coating on the inside of the lower intake. I traced it back to the throttle body. What would cause this and how can I clean up the engine? It didnt look like carbon build up. I changed the PVC valve, plugs, wires, cap and rotor.
Over time, the pcv system will pull oil into the intake system - both directly into the intake via the pcv, and through the throttle body to valve cover line - which is also part of the pcv system. Nothing to worry about as long as it's not excessive.
Isn't the line to the heater lines, and that's antifreeze, also the black buildup, if not oil, is probably from the egr, kinda like the inside of an exhaust piece, the intake cannot escape a buildup of carbon if equipped with a working egr.