I went to start my 93 Z28 last week and it wouldn't, responded like the battery was dead...but it still had power. When I went back after work to try jumping it I happened to have my spare keys instead (since I was using my other car to do the jump). Started right up and all was fine....went to take the car out later with my regular keys....wouldn't start again. It was then that i realized that the "security" idiot light was lit on the dash. Went inside and got the spare set of keys and guess what, it started right up.
So from this I assume it's a problem with the chip in the key (VATS or whatever they called it). Anyway I now have one working key. Does anyone know - must I got to GM for a new one and how much will they get me for if so?

 

Try polishing the contacts on both sides of the chip on the key that doesn't work. It's just a resistor, and any corrosion will throw the resistance reading off.

You'll get better results with this question on "General 67-02 F-Body Tech". "Fuel and Ignition" isn't the best place. I'll move it for you.

 

most lock smiths have them i just paid 20 bucks for one