1. IAC (Idle Air Control) Valve: This is the most common culprit. The IAC valve regulates the air entering the engine at idle. If it's stuck open or malfunctioning, it'll cause a high idle.
* Inspection: Locate the IAC valve (usually on the throttle body). Visually inspect it for any obvious damage or debris. A sticky or dirty valve is a likely cause.
* Cleaning: Disconnect the electrical connector. Carefully clean the IAC valve with electronic contact cleaner. Avoid using harsh chemicals. Let it dry completely before reconnecting it.
* Replacement: If cleaning doesn't work, the IAC valve might need replacement. This is relatively inexpensive and easy to replace.
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.
* Inspection: Visually inspect the TPS for damage. A more thorough check requires a multimeter to test its voltage output at various throttle positions (you'll need a wiring diagram and service manual for proper testing procedure).
* Replacement: If the TPS is faulty, it needs replacement. This is more involved than cleaning the IAC, but still relatively straightforward.
3. Vacuum Leaks: A vacuum leak can also cause a high idle. Air leaking into the intake system after the throttle body can fool the engine into thinking it needs more air at idle.
* Inspection: Carefully inspect all vacuum hoses and connections for cracks, leaks, or loose fittings. Pay particular attention to the hoses connected to the brake booster and other vacuum-operated components. Use a vacuum gauge to check for leaks if you suspect them.
* Repair: Repair or replace any damaged vacuum hoses and ensure all connections are tight and secure.
4. Mass Airflow Sensor (MAF) Sensor: While less likely to directly cause a *persistently* high idle, a faulty MAF sensor can contribute to idle issues. A dirty or malfunctioning MAF sensor can provide inaccurate air flow readings, leading to erratic idle behavior.
* Inspection and Cleaning: Carefully inspect the MAF sensor for dirt or debris. Clean it gently with MAF sensor cleaner (never use anything else).
5. Computer (PCM) Issues: Less common, but a faulty PCM can cause various engine problems, including a high idle. This is the most difficult and expensive option to troubleshoot and requires specialized tools.
Troubleshooting Steps:
1. Start with the IAC valve: Cleaning or replacing this is the easiest and most likely solution.
2. Check for vacuum leaks: These are common and relatively easy to find.
3. Test or replace the TPS: This is a more involved process, requiring testing with a multimeter.
4. Clean the MAF sensor: This is a simple preventative measure.
5. Consider the PCM as a last resort: This requires professional diagnosis.
Important Notes:
* Disconnect the negative battery terminal before working on any electrical components.
* Consult a repair manual: A repair manual specific to your 1995 Ford Mustang will provide detailed diagrams, specifications, and troubleshooting procedures.
* Safety First: Working on your car can be dangerous. If you're not comfortable performing these repairs yourself, take it to a qualified mechanic.
By systematically checking these components, you should be able to pinpoint the cause of your high idle and get your Mustang running smoothly again. Remember to test your idle after each step to see if the problem is resolved.
