How can I verify my vanos is failing?
On M52TU engine cars (98/99-00) experiencing cold weather cold start idle jolts and possible stall, the vanos intake solenoid (metal cylinder) electrical connector can be disconnected. If the idle jolts cease then the problem is most likely the vanos. On other cars the vanos needs to be removed from the engine for inspection. Once the vanos cylinder covers are removed, an inspection of the piston seals fit in the cylinders will show a loose fit and thus a seals failure. Removal of the seals from the pistons will show the inner O-rings have flat spots and a loss of elasticity. In general, a diagnosis is not necessary. The vanos Buna O-rings are deteriorating in 20k miles (32k kilometers). Thus essentially all the cars with these vanos units have deteriorated O-rings and a failing vanos.
