1. Verify the New Ignition Switch Installation:
* Correct Installation: Double-check the ignition switch installation. Even a slightly misaligned switch can cause intermittent or complete starting failure. Consult a repair manual or online diagrams for your specific Alero model to ensure everything is properly seated and connected. Wiring diagrams are crucial here.
* Wiring Harness: Inspect the wiring harness connected to the ignition switch for any damaged, loose, or corroded wires. Pay close attention to the connections – they could be loose or have poor contact. Clean any corrosion with a wire brush and electrical contact cleaner.
2. Beyond the Ignition Switch:
The ignition switch's job is to turn power *on* to other systems. The fact that it's dying immediately points to a problem with one of those systems:
* Immobilizer System: Many 1999 cars have an immobilizer system that prevents the car from starting unless it recognizes the correct key. Even with a new ignition switch and key, there could be a problem with the immobilizer system itself:
* Transponder Chip in Key: Ensure the new key has a properly functioning transponder chip. Some aftermarket keys may not have this.
* Immobilizer Module: A faulty immobilizer module could be causing the issue. This requires more advanced diagnostics.
* Fuel Pump: The car may be starting, but the fuel pump isn't supplying fuel. Listen carefully for the fuel pump whirring when you turn the key to the "on" position (before cranking). If you don't hear it, there could be a fuel pump problem, a blown fuse related to the pump, or a problem in the fuel pump relay.
* Crankshaft Position Sensor (CKP): A faulty CKP sensor prevents the engine from knowing where the pistons are and, thus, won't start or will run roughly and die.
* Cam Position Sensor (CMP): Similar to the CKP sensor, a bad CMP sensor provides incorrect timing information.
* Battery and Connections: While seemingly obvious, a weak battery or loose/corroded battery terminals can cause starting issues and immediate shutdowns.
* Alternator: While less likely to cause immediate shut-off after starting, a bad alternator won't keep the battery charged, leading to quick dying.
* Security System (Aftermarket): If you have an aftermarket alarm or security system, it may be interfering with the car's starting system.
3. Diagnostic Steps:
* Check Engine Light (CEL): Is the CEL on? If so, read the codes using an OBD-II scanner. This will provide valuable clues.
* Professional Diagnostics: If you're not comfortable with car repair, take it to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately. They can test the systems listed above, especially the immobilizer module and sensors.
Important Note: Trying to keep the car running by bypassing safety systems or manipulating wires is extremely dangerous and can damage your car further. Focus on proper diagnosis and repair to address the root cause.
