Thank you for the suggestions. I've been on vacation for two weeks but just before I left my mechanic checked the fault codes and he got code 2411 that sends us to the RPM sensor, injector sensor and a missing flywheel tooth. He told me that another customer had a simmilar problem and the symptoms were the same. In that case it was a missing tooth on the flywheel. Next week I'll check the flywheel. As soon as I find and fix the problem I'll post it here.
Thank you again.
Florin