Troubles began at 3000 miles

Thirty miles before reaching 3000 miles Jetta's motor lost almost all of its power and we had to run Jetta slowly back home from the motorway.

The reason was clogged fuel filter ( as could be expected ).
The reason for clogging the filter is vegetable oil's ability to work as detergent. Also Jetta was run empty of fuel tank a day before the troubles arose.
Just change it and go on.
The new filter should last years ( according the experience by Valmet fieldtractor 1993 - 2002 )