Help. I have an intermittent but recurring problem that Dealers cannot seem to find. My 2008 GL320 CDI will all of a sudden stop accelerating normally and seems not to upshift. Sometimes this happens while driving for extended periods and sometimes it happens after just starting from a standstill. If you stop and turn the car off for 5 minutes and restart, it behaves normally again.

The first time, this happened while traveling and so I went to MB dealer in Portland, OR area. They diagnosed dirty fuel filters and changed all filters and some other items and $1200+ later all was good...

Until 2 weeks later when it started doing it again. Took it to my local dealer here in NW Wash, and they had it for more than a week and could not find anything wrong. I asked them to have their service tech drive it for extended periods during this time and it never once happened to him.

The first time it happened, the "Check Engine" light came on. It did not come on during subsequent episodes... until today when it went into limp home mode and also displayed check engine light.

Any ideas for the tech to search for? Since MB no longer seems to hire true mechanics who can troubleshoot rather than look at computer codes or error messages, and none seem to be displayed during these episodes.