1. Vacuum Leaks:
* How it affects idle: A vacuum leak disrupts the air/fuel mixture, causing a lean condition and rough running.
* How to check: Visually inspect all vacuum hoses for cracks, splits, or disconnections. Pay close attention to the hoses connected to the intake manifold, brake booster, and other vacuum-operated components. Use a propane torch (carefully!) around suspected areas – a rising RPM indicates a leak. A more precise method involves using a vacuum gauge to measure manifold pressure.
2. IAC (Idle Air Control) Valve:
* How it affects idle: The IAC valve regulates air flow at idle. A malfunctioning valve can lead to low or erratic idle.
* How to check: This is tricky without a diagnostic tool. You can try cleaning it with a carb cleaner, but if that doesn't work, replacement might be necessary. A clogged or dirty IAC valve is a common cause of idle problems.
3. Throttle Position Sensor (TPS):
* How it affects idle: The TPS tells the computer the throttle position. A faulty sensor provides inaccurate information, leading to poor idle.
* How to check: You'll need a multimeter to check the voltage output of the TPS as you move the throttle. Consult a repair manual for the correct voltage readings. A bad TPS can also cause stalling, poor acceleration and a check engine light (if the system has one that's functioning).
4. Mass Air Flow (MAF) Sensor:
* How it affects idle: The MAF sensor measures the air entering the engine. A dirty or faulty MAF sensor can lead to a lean condition and rough idle.
* How to check: These sensors are very sensitive. The best way to check is to use a scanner that can read the sensor's output. Cleaning the MAF sensor with MAF cleaner (following the directions carefully!) is worth trying, but a faulty sensor usually needs replacement.
5. Spark Plugs and Wires:
* How it affects idle: Worn, fouled, or damaged spark plugs and wires can cause misfires, leading to a rough idle.
* How to check: Inspect the plugs for wear, fouling (black, oily, or excessively white), or damage. Check the wires for cracks or fraying. Replace as needed.
6. Distributor (if applicable):
* How it affects idle: A failing distributor cap, rotor, or ignition module can cause misfires leading to a rough idle.
* How to check: Inspect the cap and rotor for cracks, burns, or excessive wear. The ignition module is more difficult to test without specialized equipment.
7. Fuel System:
* How it affects idle: A clogged fuel filter, low fuel pressure, or problems with fuel injectors can cause a rough idle.
* How to check: Fuel pressure should be checked with a gauge. The fuel filter should be inspected for restriction. Fuel injector cleaning or replacement might be needed, but this is more involved.
Before you start:
* Check the engine codes: If your Probe has a check engine light, get the diagnostic trouble codes (DTCs) read using an OBD-I scanner (OBD-II wasn't fully implemented until later). This will give you a clue about the problem.
* Consult a repair manual: A Haynes or Chilton manual for your specific year and model will be invaluable. It will provide detailed information on testing procedures and specifications.
Important Note: Working on your car's fuel and ignition systems involves working with flammable materials and high voltage. If you're not comfortable performing these checks yourself, take your car to a qualified mechanic.
