I've got four ports on my valve covers.
Driver's front = PCV valve
Driver's rear = filler cap
Passenger rear = line from throttle body
Passenger front = ? help me

I have a breather on the passenger rear and the pcv valve on the driver's front. I want to remove them because I discovered that one of them is the source of the strange whistling noise my car make.

What is supposed to go in the passenger rear port?

 

i've never heard of any in the pass. front. can you get a pic?

 

I found this thread.
That one enlightened me a bit. I want to get the breathers off the covers. I originally put them on there about five years ago because I thought they looked cool. Recently I discovered they were having an adverse effect on performance.
I'll get a pic tonight when I get home. I recall a passenger front hole, but now you've got me second-guessing myself.

 

I would say to plug it off. I know I dont have anything there.
Actually my oil fills in the front (drivers side), because I bought some chrome powdercoated corvette valve covers.

But the passanger side is just that little elbow & pipe that goes to the throttle body.