the crankshaft sender can cause non starting, i completely forgot about this sender.
my mates golf gti had running problems and then it wouldnt start turned out to be the crankshaft sender, after it had the fault codes read.
you can test the resistance of the crank sender or sensor.
using a multi meter unclip the crank sender wire connector, the connector will look rather the same as a knock sender one on a gti.. and theres either 2 or 3 pins connect the multi meter in ohms to theses pins by either the 2 outer pins and the center pin and 1 of the outer pins..
i'm not sure which pins are correct but i think its thr 2 outer pins... any way i've check on vw vortex and theres loads of posts regarding crank position sensors....
i found this on there.............
the CPS resistance should be between 500-700 ohms...mine was around 1200-2000 cold and when the car would not start, it was infinity (open circuit).
Note: When I replaced the CPS, the new one measured about 1100 ohms, but I haven't had any problems. (2 years now)
this is on a vr6 but i would have thought that all the senders will give the same resistance...
heres the website so you may find more help on starting problems on here, some of those guys are engine fanatics and have even replaced there vr6 timing chains!!
www.vwvortex.com