1997 LeSabre- Security light in dash is constantly on. Car idles fine. Goes about 100 ft on street and dies. Sit for awhile, and start up again, light on constantly

Ok the security light is on because it isn't reading the chip pellet in the key. The problem with the is usually either bad key, bad pickup in the cylinder, or bad paskey unit. if it is the key or the cylinder then you can bypass the unit by adding a resistor to match the key resistance and attach it to the violet and white wires at the bottom of the column. I do alot of bypasses on these passkey units, it works wonderful.

Your stalling however sounds like a different problem.. since the security system only disables the starting feature and not the running of the vehicle. But with the 3800 engine the cranshaft sensor or sensor wiring, as the engine gets hot causes shorting to the computer and shuts engine down. I would look into that to solve your problems.

Is it the check engine light? You need to have the code(s) read out and pursued to repairs. Try changing out the fuel filter first. The fuel pump may also be near life end.