Common Causes:
* Dirty or Faulty Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A dirty or faulty TPS can lead to erratic idle. Cleaning it (with appropriate cleaner) is often the first step. If cleaning doesn't help, replacement might be necessary.
* Dirty or Faulty Mass Airflow Sensor (MAF): The MAF measures the amount of air entering the engine. A dirty MAF sensor will give inaccurate readings, leading to a poor idle. Cleaning it (gently, with MAF sensor cleaner ONLY – never brake cleaner!) is crucial. Replacement is necessary if cleaning doesn't fix the problem.
* Vacuum Leaks: Cracks or holes in vacuum lines can cause a rough idle. Inspect all vacuum lines for damage and replace any that are cracked or deteriorated. Pay special attention to lines connected to the intake manifold and brake booster.
* Clogged Fuel Injectors: Clogged injectors can prevent the engine from receiving the proper amount of fuel, leading to a rough idle. Cleaning them (using a fuel injector cleaner) or replacing them might be necessary.
* Ignition System Problems: Worn spark plug wires, faulty ignition coil, or failing distributor cap and rotor (if equipped) can cause misfires leading to a rough idle. Inspect these components for wear and tear and replace as needed.
* Dirty Air Filter: A severely clogged air filter restricts airflow, affecting the air/fuel mixture and causing a rough idle. Replacing it is a simple and inexpensive fix.
* Faulty Idle Air Control (IAC) Valve (if equipped): This valve controls the amount of air entering the engine at idle. A faulty IAC valve can cause rough idling, stalling, or high idle. Cleaning or replacement may be needed.
* PCV Valve: A clogged Positive Crankcase Ventilation (PCV) valve can cause a buildup of pressure in the crankcase, affecting the engine's performance and leading to a rough idle. Replacing it is inexpensive.
* Low Engine Compression: Low compression in one or more cylinders indicates worn piston rings or valve problems. This requires a compression test to diagnose.
Troubleshooting Steps:
1. Start with the easy stuff: Check the air filter, and inspect all vacuum lines for leaks.
2. Clean the MAF and TPS sensors: This is a relatively easy and inexpensive first step.
3. Check spark plugs and wires: Inspect for wear and replace if necessary.
4. Check the PCV valve: Replace if necessary.
5. If problems persist: Consider taking it to a mechanic for further diagnosis, possibly including a compression test, fuel pressure test, and/or a scan using an OBD-II scanner to read any trouble codes.
Remember to always consult your owner's manual for specific information and procedures related to your 1996 Chevy Blazer S10. Safety first! If you're not comfortable working on your vehicle yourself, take it to a qualified mechanic.
