Erratic Idling please help URGENT
 

I just fitted a boost gauge over a week ago and I'v just been out in my car which is a MY95 WRX Import. I run it on Optimax and O/B all the time and i always wait till its warmed up before you know :) . but when i was out there it started Revving up and down between 1500 rpm to 2500 rpm quite erraticly now i have checked all hoses and connections for air leaks and ther doesnt appear to be any to me anyway. any other ideas what it could be?