Looks like the vacuum tubing for the SAI system to me. I believe that plastic black and white check valve on the right of your 2nd pic will plug into that tee. The other end will plug into one of the rubber boots on the plenum. Since you are in Cali you will need to have a working SAI system to pass smog. The diagram should help, the check valve can be located anywhere not just as depicted in the diagram.
