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Discussion Starter #1
When I replaced the air filter on my 89 Si B20A5, I manually opened the intake butterfly to look down the intake channel. The intake pipe on the upstream side of the butterfly valve is clean metal, but on the downstream side the intake has a thick coat of very soft and oily carbon deposits. Car runs just fine, as far as I can tell, although it does seem to use oil.

What could be the cause? What could be the cure?

Thanks to all for your thoughts on this,
Jim
 

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The cause is the PCV system, all that gunk in there would be inside your engine clogging it up without it.
The cure is to put a well designed catch can inbetween the valve cover and the intake manifold, so that all the gunk condenses out of the air before it gets to the intake manifold.
 

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Discussion Starter #4
Thanks, I see what you mean about the source of the gunk. Does the fact that I'm getting all this coating suggest a valve guide is loose - I'm getting oil sprayed into the valve area - which then goes out the PVC tube to the intake manifold? Meaning live with it or fix the head?
 

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