Under the front unibody on the passenger sider there is a half round plastic thing with a single vacuum line attached to it. The vacuum line seems to run along the bi wiring harness on the right side front fender and disappear near the PCM.

What is this half round thing, you can only really see from the bottom when the A-shaped louvered cover is removed.

 

You mean this thing?

 

Yup, what is that thing for?

 

Its a vacuum reservoir for your HVAC. All that runs off of vacuum, you can hear it working when you turn the HVAC ***** if you listen carefully, sounds like a hissing sound. Opens and closes doors with actuators.

 

So why is it way up there, to reduce noise.

 

More than likely that was the only place they could find to put it, not much space to put things in these cars. As youve prolly noticed, things are in some odd places.