I was in mine a couple of days ago and seen it had carbon nitric(<--can't remember if that's what its called?) Build up on the rotor and cap firing prongs. Well I cleaned it off and reassembled it. Now I have a horrible skip when the car warms up. Or does the optical sensor usually go bad in them? I've double checked my almost new wires and changed out all the plugs. I'm almost certain the opti is to blame this time.

94 Z28 A4- ported heads/intake long tube headers. Egr/smog delete.

 

Virtually every component can and does fail. Rotor screw fall out, rotor and terminals corrode or burn, oil or moisture causes carbon tracking, ozone from high voltage discharge causes corrosion. Optical cam position module heat soaks or outright fails. Rust and oil blind the shutter wheel or the light emitter/receptor. Bearing fails. Harness connector corrodes, gets damaged pins, or the clip that holds it tight breaks off.

 

You may be referring to nitric acid. That can form(according to the Buick Know How video on the Opti) if there is an issue with opti not venting ozone, nitrogen and moisture from the unit.

If it's running worse after the cleaning, chances are you need a new one, but do double and triple check for wiring issues and make sure the plug wires are not in the wrong spots.