1. Verify the Vacuum Line Routing:
* Diagram: The most crucial step is to ensure all vacuum lines are routed correctly. Obtain a vacuum diagram specific to your 1989 Chevy Astro's engine (either the 4.3L V6 or the 2.5L I4). A Haynes or Chilton repair manual for your year and model will be invaluable. Online resources might also have diagrams, but always double-check against a reputable source.
* Careful Inspection: Even a small misrouting can significantly impact idle. Check each connection meticulously, ensuring a snug fit on all components.
2. Check for Leaks:
* Visual Inspection: Carefully examine all new vacuum lines for cracks, kinks, or loose connections. Look closely at the connections to the vacuum components (e.g., EGR valve, brake booster, distributor).
* Vacuum Tester: A vacuum gauge or a hand-held vacuum pump can help pinpoint leaks. Test the vacuum at various points in the system while the engine is running. A significant drop in vacuum indicates a leak. Spray a soapy water solution around connections to look for bubbling which indicates a leak.
3. Other Potential Issues (Even After Replacing Lines):
* IAC (Idle Air Control) Valve: This valve regulates airflow at idle. A dirty or faulty IAC valve is a very common cause of idle problems. It might need cleaning (with appropriate cleaner), or replacement.
* Throttle Position Sensor (TPS): A faulty TPS can send incorrect signals to the engine computer, leading to poor idle.
* Mass Airflow Sensor (MAF) Sensor: If your Astro has a MAF sensor (more likely on later models, but possible), a dirty or faulty MAF sensor can affect the air/fuel mixture and cause idle issues.
* PCV Valve (Positive Crankcase Ventilation): A clogged PCV valve can disrupt crankcase pressure and affect idle.
* Vacuum Leaks at other places: Don't overlook the possibility of leaks in other components that have vacuum connections, such as the intake manifold gasket.
* Spark Plugs and Wires: Worn spark plugs or faulty ignition wires can also contribute to an erratic idle, though this is less directly related to the vacuum system.
* Engine Computer (ECM): In rare cases, a faulty ECM could be the culprit, though this is usually indicated by multiple other problems.
4. Troubleshooting Steps:
1. Start with the vacuum lines again. Are you absolutely certain they're all correct? Refer to that diagram religiously!
2. Check for vacuum leaks. Use the soapy water test and/or vacuum gauge.
3. Clean or replace the IAC valve. This is a very common fix for idle problems.
4. Inspect the TPS and MAF (if applicable). These sensors are often easy to clean, or replacement is straightforward.
5. Check the PCV valve.
6. Inspect spark plugs and wires.
If you've addressed these points and the idle problem persists, it's time to seek professional help from a mechanic. They have access to diagnostic tools that can pinpoint the exact issue more effectively. Remember to always disconnect the negative battery terminal before working on the electrical system.
