Originally Posted by
timsrv
If the gunk inside your manifold has a trail that leads to the PCV and valve cover vent ports, then it's due to crank-case ventilation and can be normal. Intake manifolds eventually get fouled up inside due to the PCV (Positive Crankcase Ventilation) and the valve cover vent hose. These 2 larger intake ports suck the oily vapor out of the top your valve cover and recycle it back into the combustion areas. This is good because it helps prevent the formation of sludge and condensation inside the engine. It also keeps the interior of the engine at a slight negative pressure which helps inhibit external oil leaks (reduces the outward pressures on the gaskets and seals). The down side to oily vapor moving through your intake manifold is a gradual build up of oily residue inside. This build-up is very gradual but steady. Another negative aspect to crank case ventilation is over time this build-up problem becomes accelerated (due to normal engine wear). As the piston rings wear they slowly allow more and more combustion pressure/gasses to escape down and around the piston and into the crank case. The combined combustion leaks from multiple cylinders can eventually match or overcome the CFM (Cubic Feet per Minute) of vapor these vent ports can move.........and that creates a positive pressure inside the engine.
Now instead of these vent ports sucking in small amounts of vapor, they become overwhelmed by positive pressure force feeding combustion gasses into them (for a 2nd trip through the engine along with the additional vaporized oil that was picked up along the way).
One of the things you can do to check for blow-by is remove the PCV valve from the valve cover while the engine is running (leave the valve hooked up to the vacuum hose). If you can see and feel vapor puffing out of the valve cover, then you have a blow-by issue. This can be a good indication that it's time for a rebuild or at least a new set of rings.
If the residue trail inside the manifold goes back to the cold start injector, then it's possible this injector has been leaking and the build up is a result of that. Tim