Certainly! A misfire in your 2009 Chevy Express V8 while idling can be caused by a variety of issues even after replacing the spark plugs and coil packs. Here is a list of possible causes and solutions:

1. **Fuel Injector Issues:**
- **Cause:** Clogged or malfunctioning fuel injectors can lead to improper fuel delivery, causing a misfire.
- **Solution:** Use a fuel injector cleaner or have the injectors professionally cleaned or replaced if necessary.

2. **Vacuum Leaks:**
- **Cause:** Leaks in the vacuum lines can disrupt the air/fuel mixture, leading to a misfire.
- **Solution:** Inspect vacuum hoses for cracks or disconnections and replace any damaged hoses.

3. **Faulty Mass Air Flow (MAF) Sensor:**
- **Cause:** A faulty MAF sensor can send incorrect data to the engine control unit (ECU), disrupting the air/fuel ratio.
- **Solution:** Clean the MAF sensor using a specialized cleaner or replace it if cleaning doesn't resolve the issue.

4. **Dirty or Faulty Idle Air Control (IAC) Valve:**
- **Cause:** A dirty or malfunctioning IAC valve can cause improper idling.
- **Solution:** Clean the IAC valve. If cleaning doesn’t help, consider replacing it.

5. **Faulty Oxygen Sensors:**
- **Cause:** Oxygen sensors provide feedback to the ECU about the air/fuel mixture. Faulty sensors can lead to incorrect adjustments.
- **Solution:** Test the oxygen sensors and replace any that are malfunctioning.

6. **Engine Compression Issues:**
- **Cause:** Low compression in one or more cylinders due to valve, piston, or gasket issues can cause a misfire.
- **Solution:** Perform a compression test to check for low compression. Address any issues with valves, pistons, or gaskets as needed.

7. **ECU Problems:**
- **Cause:** Software or hardware issues with the ECU can result in improper engine management.
- **Solution:** Have the ECU scanned for error codes and software updates. Consider reprogramming or replacing the ECU if necessary.

8. **Exhaust Gas Recirculation (EGR) Valve:**
- **Cause:** A malfunctioning EGR valve can cause rough idling and a misfire.
- **Solution:** Clean or replace the EGR valve.

9. **Wiring and Connectors:**
- **Cause:** Damaged wiring or poor connections to the spark plugs, coils, or injectors can cause intermittent misfires.
- **Solution:** Inspect the wiring harness and connectors for damage or corrosion and repair or replace as needed.

10. **Throttle Position Sensor (TPS):**
- **Cause:** A faulty TPS can send incorrect signals to the ECU, resulting in improper fuel delivery.
- **Solution:** Test the TPS for correct operation and replace if faulty.

11. **Crankshaft or Camshaft Position Sensors:**
- **Cause:** Faulty sensors can cause timing issues, leading to misfires.
- **Solution:** Test the sensors and replace if any are found to be faulty.

You might want to use an OBD-II scanner to check for any diagnostic trouble codes (DTCs) that can give you a more specific idea of the issue. This can significantly reduce the time spent diagnosing the problem. If you identify specific codes, addressing those issues first can help resolve the misfire more effectively.