[Vwdiesel] Engine won't turn off?

[Bud S]

After I turn the ignition switch off the engine still runs.  I checked 
to see if voltage was still on the fuel shutoff solenoid on the IP and 
there is no voltage, so the circuit is working fine.  Can the shutoff 
plunger become magnetized over time and not fall back to stop fuel flow?

The other thing I have noticed is the crappy fuel I've been getting over 
the last year or so.  I have a glass filter before the oem one and you 
can see the crud pile up.  The last tank full, it seems like there was 
some varnish type residue in it.  I've since changed the filters and 
gotten a new tank of diesel and it seems to be clear so far.

Thanks,
Bud