Lately my engine had been wanting to idle much higher than it set, so I got to checking for vacuum leaks and ran across the line that comes out of the firewall that goes to the diaphram for changing the air flow from bottom to front to defrost. I tryed to pull a vacuum on it and it wouldn't. it just blew air right through it. isn't that supposed to pull atleast some vacuum? The air shouldn't just go right through it right?