* Idle Air Control (IAC) Valve: This valve regulates air flow at idle. A dirty or malfunctioning IAC valve is a common cause of high idle or erratic idling. Cleaning it (with carb cleaner, for example) is often a simple fix. If cleaning doesn't work, it may need replacement.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can cause incorrect fuel/air mixture, leading to high idle. It usually needs replacement.
* Mass Air Flow (MAF) Sensor: Measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to incorrect fuel delivery and high idle. Cleaning it (carefully!) might help, but replacement is often necessary.
* Vacuum Leaks: Leaks in vacuum lines can disrupt the engine's idle control system. Inspect all vacuum lines for cracks, holes, or loose connections.
* Dirty Throttle Body: Buildup of carbon deposits on the throttle body can interfere with smooth idle. Cleaning the throttle body is recommended.
* Faulty Engine Control Module (ECM): While less likely, a problem with the ECM (computer) can cause a variety of issues, including erratic idling. This is a more involved and expensive diagnosis/repair.
* Transmission Problems (Less Likely): In rare cases, a transmission issue *might* indirectly cause a higher idle, though this is less common than the other issues mentioned.
Troubleshooting Steps:
1. Check the simplest things first: Ensure the car's not accidentally in gear (automatic transmission), the brake is not slightly engaged (some cars have systems affected by this), and that there's nothing physically restricting the throttle.
2. Check the engine compartment: Look for any obvious vacuum leaks, loose connections, or damaged wires.
3. Clean the IAC valve and throttle body: This is often the easiest and cheapest first step. Numerous online tutorials show how to do this.
4. Check for diagnostic trouble codes (DTCs): Many 1990 Mazdas have a method for retrieving diagnostic trouble codes from the ECM. This can point to a specific problem. Consult your owner's manual or an online resource specific to your vehicle's year and model.
5. Professional Diagnosis: If you're not comfortable tackling the above, take it to a qualified mechanic. They have the tools and expertise to diagnose the issue accurately and make the necessary repairs.
The revving could be a minor issue easily resolved by cleaning, or it could indicate a more serious problem that requires professional attention. Start with the easier steps, and if the problem persists, get it checked by a mechanic.
