Today I visited my friends at Bavarian Workshop – a small service center, which specializes in the repair of BMW vehicles. Current patient: E66; 745Li with N62B44 engine.

The engine had abnormal idle, which normalized, only when Valvetronic was disconnected.


For the engine, preventive maintenance was done, gaskets were replaced, to avoid the coolant leaking in the oil (yes, also this problem was identified, when the repair was started). From Valvetronic hub, only HVA were replaced.


Here, Rough run data after replacing HVA:

For this SW, +9.5 units correspond to the disconnected cylinder. As we see, larger differences from ideal are:

  • cylinder No.2: 0.59, which corresponds to mechanical efficiency, increased for +6.2%;
  • cylinder No.4: +0.87, which corresponds to mechanical efficiency, decreased for -9.2%.

Such correct results of the engine performance were reached by the opening of the inlet valves for 0.35mm.

Note: for the engines, which are equipped with Valvetronic, differences of mechanical efficiency of cylinders, which are less than +/-10%, DME considers as allowed and don’t try to correct. Accordingly – if the mechanical efficiency of all cylinders fits into a range of +/-10%, the engine performs as it is supposed to.


Subjectively, the engine now runs evenly, without permanent vibration, all problems in idle have disappeared. This is already numerous engine, equipped with Valvetronic, whose performance (normal idle and evened mechanical efficiency of cylinders) is restored, simply replacing HVA.

Experience of repairs confirms – the basis of all problems of Valvetronic: HVA problems, not microscopic wear or other undetectable defects.