I just had this exact same problem. When it first happened I even tore up my fenders when the tires rubbed. After a month in the shop and alot of head scratching.. it ended up being the level control valve which was about $1400 just for the part and they had to ship it in from germany. Another symptom that I noticed on mine is that when it would come back up after starting the engine.. the hydraulic resevoir would empty of fluid and then when the car would be turned off the resevoir would fill back up