I've had some time to disassemble and clean things, and I think my oil issue was caused by the intake gaskets being positioned too far down on the front ports. When it goes back together I'm going to remove the plastic locating pegs and glue the gaskets to the heads with RTV overnight before final installation to make sure they're where they're supposed to be. The oil infiltration problem was primarily on the 1 & 3 ports where the gasket misalignment was most evident, and the rest could have just been normal PCV function.

Quote Originally Posted by LeMarky Dissod View Post
So far, I have not seen a single LT1 inlet manifold that has had its idlespider properly cleaned during a socalled cleaning. This will definitely have an impact on your idle, as it does for us all.
My intake is the 5 plug design identical to the one posted back on page 5 by kur4o [link]. I blew some compressed air through the idle air plenum and was able to feel some coming out of all four of the tapped plug holes (the center hole connects to the EGR passage). There is a bit of crud in these passages (far more in the EGR passage) so I decided to soak the manifold in some diesel fuel before taking a pressure washer to it tomorrow. I wasn't able to find a disposable pan big enough to submerge the portions I wanted to clean so I flipped it over and started pouring diesel into the idle plenum. Immediately I noticed this was connected directly to the PCV inlet, so I capped it off. I then poured what I felt was an alarming amount of fuel into this plenum. Eventually fuel started to trickle out of the IAC inlet hole below (actually above) the primary throttlebody inlets. I was shocked at how much fuel this passage holds, and that the level of liquid while stabilizing only 1/8" below the port orifice holes was barely trickling out of the IAC inlet that by my estimation is at least 0.8" lower (intake inverted). I suppose it would take a couple x-rays to figure out what's going on here but it seems this plenum has a complex internal layout.

I'm seriously contemplating enlarging the #1 idle feed hole. All the others are 15/64" / 6mm, but this one is 5/32" / 4mm. I'm thinking I'm going to go to 13/64" / 5mm. Anyone have any thoughts on this?