That sensor is the pick up coil (or the crank position sensor). It is a n actual coil (small in size) that induces current when a small steel peices on the dumper passclose to it. It causes the computer to fire the coils. Usually this unit fails from heat, corrosin, etc. and it usually results in hard starting, soothy plugs and hard miss at different speeds. That might as well be your problem,. Did you scan the computer for codes? Sometimes when that sensor wont cause any codes unless it completely shorted out and dead. (keep in mind your ignition systems is still kinda operational), but instead different codes for ignition can pop out.
I would defenatly see what the computer is registering. But the crank sensor is defenatly the first thing on the list. (they should not be very expensive)