If your Focus idles rough and stalls or sets a lean bank code it is 99% of the time the bottom elbow on the EGR hose. Follow the EGR hose from the valve cover down the back of the engine and into the throttle body. Their is a 90 degree reducing elbow that connects to the main vac source, This elbow will be very soft from bypass gasses. This is the source of your vac leak. Ford sell the whole hose for $50. You can plug it off if you want to save $50. Be sure and remove the battery cable for 5min after you fix the hose so the computer will reset and relearn. Any questions? snipped-for-privacy@yahoo.com