What can cause (NE) CAS frequency to be to high?
 

I've been helping a friend of mine try to figure out whats causing his horrible stuumble/hesitation at anything but very light load. A couple days ago we hooked it up to an oscilloscope and viewed crank angle senor signal frequency. The (G) sensor signal tested ok, but (NE) sensor frequency was about double what it should be. It should have been about 60hz at idle and 200hz by 2500rpm, but it was reading about 400 by 2500rpm. The car wont idle below 1000, but at 1000rpm its at about 150hz.

Does anyone have any experience w/ crank sensor problems or have any idea what could be causing the high sensor frequency?