My MY96 WRX has recently started to tick over at about 2000 rpm after my usual run along the motorway. I dip the clutch every few miles to see if the problem has appeared, it only seems to happen when I get onto the slip road at the end of the motorway. My dealer has lubricated the throttle actuator and has cleaned the throttle body, but the problem is still there. Has anybody else had this happen or know the cure?