Electrical System Checks:
* Wiring Harness: A common problem in older vehicles is damaged or corroded wiring, particularly in the area around the ignition switch and the battery. Carefully inspect the wiring harnesses for any breaks, chafing, or corrosion. Pay close attention to the main power cables going to and from the battery.
* Ignition Switch Wiring: Even with a new ignition switch, the wiring *to* the switch could be faulty. Double-check all connections related to the new ignition switch.
* Starter Relay and Solenoid: These are critical components in the starting process. A bad relay or solenoid can cause intermittent starting issues. You might be able to hear a click from the relay when you turn the key – if you don't hear anything, that's a strong suspect.
* Neutral Safety Switch (Automatic Transmission): If your Impala has an automatic transmission, this switch prevents the car from starting unless the gear selector is in Park or Neutral. A faulty switch will prevent starting.
* Security System (if equipped): Does your Impala have a factory or aftermarket security system? A malfunctioning system could be interfering with the starting process. Try disabling the system (if possible) to see if that resolves the issue.
* Voltage Drop Test: Use a voltmeter to check the voltage at various points in the starting circuit (battery, ignition switch, starter motor) while someone tries to crank the engine. A significant voltage drop indicates a problem with the wiring or a connection.
* Grounds: Poor ground connections can cause all sorts of electrical gremlins. Check the main ground cables from the engine and the battery to the chassis. Clean the connection points with a wire brush.
Other Possibilities (Less Likely but Worth Considering):
* Fuel Pump: While less likely to cause an *intermittent* starting problem, a failing fuel pump could lead to a situation where the car sometimes starts and sometimes doesn't. Listen for the fuel pump whine when you first turn the key to the "on" position (before cranking).
* Immobilizer System: Some vehicles have an immobilizer system that prevents the car from starting unless the correct key is used. If you've had key issues, this might be worth investigating.
Troubleshooting Steps:
1. Start with the easiest checks: Visually inspect the wiring harnesses, connections, and ground cables. Clean any corroded connections.
2. Check the starter relay and solenoid: These are relatively easy to test and replace if needed.
3. Use a voltmeter: This is the most effective way to pinpoint electrical problems.
4. Consult a repair manual: A repair manual specific to your 2002 Chevy Impala will provide detailed diagrams and troubleshooting procedures.
If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic for diagnosis and repair. Continuing to try to start a car with intermittent starting issues can further damage components.
