Double vanos system on several models of BMW from 1999 to 2006, have defective vanos systems. The E39 double vanos (variable valve timing unit) has a malfunction problem. This double vanos can be found on 6-cyl engines M52tu, M54, and M56, found in several model cars, E39, E46, etc, years 99-03. The malfunction symptoms are almost all subtle and mostly go unnoticed. They include lower gas mileage, lower performance, degraded emissions control, and possibly others. The M52tu engine (99-00) has one further malfunction symptom which is far from subtle. It occurs on cold weather cold engine starts and takes the form of repeated engine attempted stalls and possibly a complete engine stall. The engine rpms drop dramatically and then recover. This then repeats after a few seconds of steady idle. The problem can be more definitively diagnosed by disconnecting the vanos intake or exhaust solenoid electrical connector.

- Miramar, FL, USA