Instead of adjusting the idle yourself, you should diagnose the underlying *cause* of the idle problem. A rough or incorrect idle speed usually points to one of several problems:
* Dirty or Faulty IAC Valve: This valve controls the air bypassing the throttle plate to set the idle speed. It can become dirty, sticking, or fail entirely. Cleaning it (carefully, following online guides specific to your truck's IAC) or replacing it might solve the issue.
* Vacuum Leaks: Leaks in the vacuum system can affect idle. Check all vacuum hoses for cracks or disconnections. Pay close attention to hoses connected to the brake booster, PCV valve, and the manifold.
* MAF Sensor (Mass Airflow Sensor): A dirty or faulty MAF sensor will send incorrect information to the computer, affecting the fuel mixture and idle. Cleaning it (carefully, following specific instructions) or replacing it is a possibility.
* Throttle Body: A dirty throttle body can cause erratic idle. Cleaning it with throttle body cleaner is often a good first step.
* TPS Sensor (Throttle Position Sensor): This sensor tells the computer the throttle position. A faulty TPS sensor can cause a variety of problems, including idle issues.
* Computer Issues (PCM): In rare cases, the Powertrain Control Module (PCM) itself could be the problem. This is less likely but should be considered if other components are ruled out.
* Engine Problems: More serious mechanical issues like a vacuum leak inside the engine, issues with the ignition system, or problems with the fuel injectors can also affect idle.
What you SHOULD do:
1. Consult a Repair Manual: Get a repair manual specific to your 1996 Chevy Silverado. This will provide diagrams and detailed instructions. Haynes and Chilton manuals are readily available.
2. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any trouble codes stored in the PCM. These codes can pinpoint the problem. Auto parts stores often offer free code reading services.
3. Clean the Throttle Body and IAC Valve: This is often a simple and effective first step. Use a dedicated throttle body cleaner and follow instructions carefully.
4. Inspect Vacuum Hoses: Visually inspect all vacuum hoses for cracks, leaks, or disconnections.
5. Professional Help: If you are not comfortable performing these tasks yourself, take your Silverado to a qualified mechanic. Improperly diagnosing or attempting repairs can lead to more expensive problems.
In short: Don't try to adjust the idle directly. Focus on diagnosing and fixing the underlying problem. There is no simple "idle adjustment screw" on your truck.
