* Throttle Body: Even with a new IAC, a dirty or faulty throttle body can cause rough idle. Clean the throttle body thoroughly with throttle body cleaner, paying close attention to the passages. Make sure the throttle plate moves smoothly.
* Mass Airflow Sensor (MAF): A dirty or failing MAF sensor provides inaccurate air/fuel readings to the engine computer, leading to a rough idle. Try cleaning the MAF sensor with MAF sensor cleaner (use only MAF cleaner; other cleaners can damage it). If cleaning doesn't help, it might need replacement.
* Spark Plugs and Wires (again): While you've mentioned replacing the wires, double-check the spark plugs. They might be fouled, worn, or the wrong heat range. Inspect them carefully for wear and tear. Even new wires can have a faulty connection. Make sure all connections are secure.
* Ignition System: Consider the ignition coil(s) and ignition module. A weak coil or failing module can cause misfires, leading to a rough idle, particularly when cold.
* Crank Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation. A failing CKP sensor can cause a rough idle, especially when cold, as the engine struggles to establish proper timing.
* Fuel Pressure Regulator: A faulty fuel pressure regulator can cause inconsistent fuel pressure, affecting the idle.
* Vacuum Leaks: Check all vacuum lines for cracks, leaks, or loose connections. A small leak can significantly impact engine performance, especially at idle. Use a vacuum gauge if possible to check for leaks.
* Oxygen Sensor(s): Though less likely to directly cause a rough idle at startup, a bad O2 sensor can contribute to a poor air-fuel mixture, impacting the overall running condition.
* Coolant Temperature Sensor: An inaccurate coolant temperature sensor can cause the computer to send incorrect fuel mixture information, worsening the rough idle when cold.
Troubleshooting Steps:
1. Check for trouble codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the engine computer. These codes can pinpoint the problem area.
2. Systematic approach: Work through the list above, testing or cleaning one component at a time. After each repair or cleaning, start the engine and check for improvements before moving to the next item.
3. Professional Diagnosis: If you've checked all of the above and still have a rough idle, it's time to take your Blazer to a qualified mechanic for a professional diagnosis. They have specialized tools and expertise to pinpoint the issue.
Remember safety first. Always disconnect the negative battery terminal before working on any electrical components. If you're not comfortable working on your vehicle's engine, it's best to leave it to a professional.
