The problem has to do with the car idling in the low rpm range, 200 to 500. This started to occur after I installed the plenum Sunday afternoon. I popped the hood and there seems to be air coming from the plenum. Is this normal? Did I f*ck up the install or is this normal? Everything seems to be normal while I'm driving.

 

you have an intake leak !!! bad bad bad....

You either have a defective plenum, or you screwed up the install.
Recheck your install... did you put all the bolts and hoses back ?
Did you torque it correctly, etc....

The rough/low idle is a result of air being sucked in that the engine doesn't know about... i.e. it didn't come in through the intake so it is not giving the proper fuel.

You can isolate the leak with a sray can of something like cold start spray from the auto store... (stuff is flamable so be careful).

But if you spray a little in an area and the idle jumps up/smooths out... that is where the leak is.