Can anyone tell me what this is part is called on my 97 Seville STS? Is there suppose to be something plugged into the side? It is located behind the motor on the driver side. I changed the spark plugs on my STS today and noticed that there was something that wasnt connected to this part. I think this is why my sts is still a little shaky and why i keep getting the service idle control system message Thank you!

 

looks like evap solenoid, nothing plugs in there