Hello. Possibly I could get some direction as where to go from here. I have a 2005 xjr with all new Bilstein air springs. All codes have been eliminated but the front still drops over night with battery connected. Once battery is disconnected the car stays level for weeks. could this be a bad height sensor? I put the battery cable on for a minute the other night and right away one of the valves in trunk chirp to release air. I quickly removed the neg cable.

 

According to the wiring diagram you have two sensors on the front if you can connect a code reader with live data you could possibly see if you have a faulty sensor. There is a cycle the air suspension goes through when you switch off and it maybe one of the cycles are not working properly and lowering the car

 

The vehicle automatically wakes itself daily to adjust height. It's that way by design.