Re: Black coating in throttlebodies 954rr
Too bad you didn't shoot a pic first. Show the part wiped? I'm going to take a guess.
1. A layer of slippery silicone as used for the piston skirts on some models? So in this case, a part is going to have a recess for this layer. Do you feel a step there as if something needs to be filled back in?
2. Carbon build? The intake and valves are at an overlap (both open at the same). So both fuel and spent are circulating at that time in the chamber. One is a liquid, the other a gas. Add, 'for every action' that air did get sucked in, but now it's a spit-back into the throttle body. What's left of you wiping off is a solid (black carbon soot-build)
3. Without a photo of the area... I don't see how/why they have a layer on a plate that is just in the way of air flow. The shafts I can see, but a fly?