1. Idle Air Control (IAC) Valve: This is the most common cause. The IAC valve controls the amount of air entering the engine at idle. A dirty or malfunctioning IAC valve can cause a high idle.
* Troubleshooting: Try cleaning the IAC valve with carburetor cleaner. Make sure to disconnect the battery negative terminal before doing so. If cleaning doesn't work, it might need replacement.
2. Throttle Position Sensor (TPS): The TPS tells the computer the throttle's position. A faulty TPS can send incorrect signals, leading to a high idle.
* Troubleshooting: This usually requires a multimeter to test the voltage output of the TPS at various throttle positions. A faulty reading usually indicates a bad sensor needing replacement.
3. Vacuum Leaks: Leaks in the vacuum system can cause the engine to receive more air than intended, resulting in a high idle.
* Troubleshooting: Visually inspect all vacuum hoses and connections for cracks, splits, or loose fittings. Pay close attention to the brake booster hose, PCV valve hose, and the hoses connected to the intake manifold. You can use a vacuum gauge to check for leaks if you're comfortable with that.
4. Mass Airflow Sensor (MAF) Sensor (if equipped): While less likely on a '95 Ranger 2.3L (which might have a simpler system), a dirty or faulty MAF sensor can affect the air-fuel mixture, potentially leading to a high idle.
* Troubleshooting: Clean the MAF sensor carefully with MAF sensor cleaner (never use anything else). Replacement might be necessary if cleaning doesn't resolve the issue.
5. EGR Valve: The Exhaust Gas Recirculation valve might be sticking open. This will alter the air-fuel mixture.
* Troubleshooting: This can often be tested by disconnecting the vacuum line to it and observing if the idle changes. If it does, the EGR valve might need cleaning or replacement.
6. Computer Issues: While less common, a problem with the Engine Control Module (ECM) or its programming could cause a high idle. This is a more advanced issue requiring diagnostics.
7. Throttle Body: A dirty or sticky throttle body can hinder its smooth operation, potentially leading to a high idle. Cleaning the throttle body with throttle body cleaner is a good first step.
Before you start:
* Check the battery terminals: Loose or corroded terminals can cause erratic electrical signals.
* Check your engine coolant level: Low coolant can trigger high idle in some vehicles to prevent overheating.
Recommendations:
1. Start with the easiest and cheapest: Clean the IAC valve and the throttle body. Inspect all vacuum hoses.
2. Use a multimeter: If you have a multimeter, testing the TPS is the next logical step.
3. Consult a repair manual: A repair manual specific to your 1995 Ford Ranger 2.3L will provide detailed diagrams and troubleshooting procedures.
4. Professional Diagnosis: If you're not comfortable with automotive repair, take your Ranger to a qualified mechanic for diagnosis and repair.
Remember safety first. Disconnect the negative battery terminal before working on any electrical components. If you're unsure about any step, it's best to seek professional help.
