I have a 1989 Passat that I've fitted a tdi 1900 engine & similar engine management from a mk3 golf tdi (uses bosch system / fly-by-wire as on 300tdi D1 auto??)
in december it refused to start so I tried all kinds including +12v to the stop solenoid on the injection pump, still wouldnt start
fault code reader later said that it was the solenoid so I changed it (10 mins job, had a spare as they are about £7

)
Bearmach Land Rover Range Rover 1 Fuel Stop Cut Off Solenoid Switch RTC6702
http://www.ebay.co.uk/itm/261598255781?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
£6.94
you can take the solenoid from the pump (24mm spanner for body & 8mm for wire, carefull as there is an 'O' ring in there & a spring on top of the plunger?) then remove it's plunger & re-fit the solenoid body then see if it starts up & runs, to stop the engine you should be able to use the ignition key as normal as the ecu will drop the fueling & timing to stall the engine - the solenoid is supposed to be a left-over from older pumps & a 'last-resort' to stop running
hopefully something like that anyway
Rich.