Something preventing idle adjustment points to a problem *within* the system, not a simple adjustment. The "something in the hole" likely refers to a blockage or malfunction within a component involved in the idle air control system.
Here's a breakdown of troubleshooting steps:
1. Check for Vacuum Leaks: A significant vacuum leak can cause erratic idle. Inspect all vacuum hoses connected to the throttle body, intake manifold, and other components for cracks, holes, or loose connections. Pay close attention to the hose connected to the Idle Air Control (IAC) valve.
2. Inspect the IAC Valve: The IAC valve is crucial for controlling idle speed. It's often a small electric motor near the throttle body. Check for debris in the valve passage or if it's sticking. Sometimes, cleaning it with carburetor cleaner (following the cleaner's instructions carefully) can resolve the issue. However, a faulty IAC valve will require replacement.
3. Throttle Position Sensor (TPS): A faulty TPS can send incorrect signals to the PCM, affecting idle speed. A dirty or damaged TPS needs cleaning or replacement. A multimeter can check for correct voltage output.
4. Mass Airflow Sensor (MAF) Sensor: While less directly involved in idle speed, a dirty or faulty MAF sensor can still negatively impact it. Clean the MAF sensor carefully with MAF sensor cleaner (following instructions precisely – avoid touching the sensor element).
5. Check the PCM: While rare, a faulty PCM could be the culprit. This is a more advanced diagnosis and often requires professional help.
6. Coolant Temperature Sensor: An inaccurate coolant temperature reading can cause the PCM to adjust idle incorrectly. This sensor can be tested with a multimeter.
7. Clean the Throttle Body: A dirty throttle body can hinder smooth operation. Carefully clean it with throttle body cleaner, paying attention to the throttle plate and passages. Avoid spraying cleaner directly onto the TPS.
If you're still stuck after these checks:
* OBD-II Scanner: An OBD-II scanner can read diagnostic trouble codes (DTCs) from the PCM. These codes provide valuable clues about the problem. Most auto parts stores can scan your vehicle for free.
* Professional Mechanic: If you're not comfortable with these diagnostic steps, it's best to take your Suburban to a qualified mechanic. They have the tools and expertise to pinpoint the exact cause and make the necessary repairs.
Important Note: Never attempt to adjust the throttle stop screw on the throttle body. Doing so can cause damage and worsen the problem. The PCM controls the idle speed, and messing with this screw will likely cause problems with driveability and possibly damage the engine.
