can anyone tell me what this valve does pleeeease

CAN ANYONE TELL ME WHAT THIS VALVE DOES AND WHY IT HAS BEEN DISCONNECTED,THE PIPES THAT ARE SUPPOSED TO GO TO IT HAVE BEEN BLANKED OFF,I DONT WANT TO CONNECT IT BACK UP BECAUSE I DONT KNOW WHICH PIPES GO WHERE OR IF IT WORKS,iIT IS POSISITIONED ON THE O/S FRONT SHOCKER MOUNT ,WHEN I START THE ENGINE IT IDLES AT 2000RPM AND AS IT WARMS UP IT DROPS TO 1000 AS IT SHOULD ALL HELP WILL BE MUCH APPRIECIATED
CHEERS
DAN COOKE