I had this same problem. If you follow the lines you will see "elbows", in those elbows there are "check valves". In mine those valves were sticking and I tried to clean, oil, and even boiled them but they still stayed stuck or inconsistent. A simple fix though, pull one off and take it to the local auto store and compare it to a "vacuum elbow" and just replace all of them. I have done this in august of last year and haven't had a problem since, Mine was actually blowing the line off the reservoir. GL, Joe