The idle speed is primarily controlled by the PCM based on several factors including engine temperature, throttle position, and various sensor inputs. If your Blazer's idle is too high or too low, the problem likely lies elsewhere in the system. Here's a breakdown of troubleshooting steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the PCM. These codes will point you toward the likely culprit. Common issues leading to incorrect idle speed include:
* IAC (Idle Air Control) Valve Problems: This valve controls the amount of air entering the engine at idle. A dirty or malfunctioning IAC valve is a very common cause of idle problems. Cleaning it (with appropriate cleaner) might solve the issue. Replacement is necessary if cleaning doesn't work.
* TPS (Throttle Position Sensor) Issues: A faulty TPS sends inaccurate signals to the PCM, affecting idle control.
* MAP (Manifold Absolute Pressure) Sensor Problems: An inaccurate MAP sensor reading also interferes with the PCM's idle control calculations.
* Vacuum Leaks: Leaks in the vacuum system can cause erratic idle. Inspect all vacuum hoses and connections for cracks or disconnections.
* Mass Airflow Sensor (MAF) Issues: A dirty or faulty MAF sensor can affect air/fuel mixture and thus the idle.
2. Check Engine Condition: Make sure there aren't any other underlying mechanical problems, such as:
* Low compression in one or more cylinders.
* Internal engine leaks (vacuum or coolant).
* Ignition system problems (spark plugs, wires, distributor cap and rotor).
3. Professional Help: If you're not comfortable diagnosing and repairing these electrical and mechanical components yourself, take your Blazer to a qualified mechanic. Attempting to adjust the idle without understanding the underlying cause could result in further damage and expensive repairs. They have the tools and expertise to properly diagnose and fix the issue.
In short: Don't try to manually adjust the idle speed on a 1995 Chevy Blazer. Focus on diagnosing and fixing the underlying problem indicated by DTCs and thorough inspection.
