hello, i'm searching for help.

I'm the owner of a jaguar xf s 3l v6 275hp 2009 with 110K miles.
Recently the engine start to misfire regulary, every 10 or 15 secondes the t/min is going down to 500t/min for 2 secondes and back to normal, like something block the air or fuel, while i was driving then dies. The car start again after then do the same process. misfire 3 or 4 times then dies. Even when not driving.
There's no warning or default light on the dashboard.

I bring it to the garage but the mecanics are unable to find where the problem is coming from. (i'm in France and the garage is not a Jaguar specialist...).
They change the gazoil filter but no good results. they said that it's might coming from the injection system but need to undo a part of the engine to check it with no guarantee of result..
Is someone able to give me some good tips that i can communicate to the mechanic?
Thanks !

 

Have you checked the OBD to see there are any DTC codes being thrown? I would expect to see a DTC if the engine is stalling out like that.

 

They probably can't or didn't look for Jaguar-specific explanatory codes