Did you check with soapy water? You are leaking air somewhere and you need to find it. Intermittent or not, it is not normal operation. Even if my X sits for 5 days with no batt connection, she stays up without a problem. Run the solution on the lines, the bags, and around the wheel well. She may be intermittent for now, but you are going to wake up one morning and the rear is going to sit on the frame. Then your ride is really going to suck.

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2011 E70 50i M Sport