Socals right......a dime will work fine....
WIth intermittent spark (assuming reference sensor is installed at right height) I am thinking your wiring could be giving you troubles. The boots on these harnesses are BRUTAL. YOu cut back the rubber and you will see corroded connections........
Here is what you will see with an oscilloscope...
Here is a pick of my old sensor with a washer glued on.....and the reference pin to the left of it...
