I had a P0455 code. They made a vacuum test and there was no vacuum at all. Then they triggered the valve a couple of times, and then the vacuum was ok. They weren't able to reproduce the problem.

The thing is that last time I had that exact same problem, they changed the shut off valve (probably they did not have to)

The MB tech at the dealer passed 3.5 hours on the problem and could not find anything

Does someone have an idea of what other cause could do this problem? Maybe a connection to the valve?

Thanks

Etienne