I think my tach wire has a bad connection somewhere, because very randomly and sporadically, my car will start going from 0 rpm to 1500 rpm and even higher just jumping around like crazy, and then it'll usually stall. One time when it stalled, the tach on the dash was swinging around like a madman, and it stuck at 6900rpm when the car stalled. I know the engine wasn't actually at 6900rpm though, because I was in 6th gear on the highway, so I'd have been going about 200 if it really were at that rpm.

The only other thing I can think of is the optical eye giving back crazy readings from the optispark, but is the tachometer reading based on the optical eye, or based on something more standard?

It's definetly an electrical problem... I'd just like to know where I should look before I start ripping things apart. I just put an entirely new optispark in maybe 5,000 miles ago (at most).

Could the crappy security system that came installed in the car be causing this kind of behavior, if one of it's connections to the tach wire were faulty?

Any opinions would be much appreciated, I've got a long trip to make this weekend, and I'd rather not be stuck every few hundred miles jiggling all the wires under my dash and under my hood, hoping something makes this electrical demon dissapear again.

There doesn't seem to be any relationship between coolant temp, oil pressure, etc and when this happens. It's happened 4 times now, 3 of them were city driving, one was highway.

 

My guess: Either opti (oh no) or the connections between there and the pcm. The "tach" wire itself couldn't really cause problems if you are talking about the signal from the pcm to the dash. But anything up to the pcm would cause the car to stall and made the tach act up.

I would chech the opti wiring harness first. Those things mess up and the connections can get crappy.