hmmm... I read topic with your problem, but it seems your rpm signal was more noisy than mine. I have "saw like" signal only when misfiring, usually just before it starts, and when I release accel pedal, continues for a little bit and then goes normal...
I haven't tried different polarity of VR, but i surely will. How I found "correct" polarity? Put led diode on two pins that are not shield ground, moved screwdriver to the center of the sensor, and from center of sensor, and when diode blinks when I move screwdriver TO center (if not, I change polarity of led), I assume thats correct polarity. Is this correct?