are you refering to the 2nd black piece in the pic rockin rick attached?? if so that is a fitting to attach the hose that comes off the oil fill neck to the cold ait like it was on the stock intake...
..and the oil splatter is because when the pcv vents the crankcase pressure...it sometimes brings oil up with it...and it goes through that hose into the intake back into the manifold....
Their are 2 black pieces. The one seen is the IAT. The other is a plastic 3/8" NPT to 1/2" barb fitting for the vac line to the valve cover. The splatter comes from that hose to the valve cover. This is part of the PCV system. The airflow through this hose is actually bi-directional. Sometimes it goes into the valve cover, sometimes it goes out of the valve cover and into the intake tract.
When I took that pic, I had only ran the car about 30 mins on the brand new motor, but the rubber hose to the VC was not cleaned out from the previous 150,000 miles. I then cleaned the hose out and remade the PVC intake tube. After another 4 hours of run time, there wasn't hardly any splatter like shown in the pic. But it may once again do that if the hose gets a chance to build up sludge...