The reasons for a persistent check engine light in a '99 Miata are numerous and can range from minor to major issues, including:
* Loose or damaged gas cap: This is often the simplest and cheapest fix. A faulty gas cap can allow fuel vapors to escape, triggering the light.
* Oxygen sensor issues: Oxygen sensors monitor the exhaust gases. A failing sensor can cause inaccurate readings, leading to the light. This is a relatively common problem in older Miatas.
* Mass airflow sensor (MAF) problems: The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can throw off the air/fuel mixture, triggering the light.
* Catalytic converter issues: A failing catalytic converter is a more serious and expensive problem.
* Spark plugs or ignition system problems: Worn or faulty spark plugs, ignition coils, or wires can cause misfires, triggering the check engine light.
* PCV valve problems: A malfunctioning positive crankcase ventilation (PCV) valve can lead to various engine issues and trigger the light.
* Various sensor problems: Numerous other sensors (e.g., crankshaft position sensor, camshaft position sensor) can cause the light to illuminate.
To determine the *cause* of the light, you need to:
1. Get the Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner (available relatively inexpensively at auto parts stores) to read the codes stored by the car's computer. These codes will give you a much better idea of the specific problem.
2. Interpret the codes: Once you have the codes, look them up online (many free resources are available) or consult a repair manual.
3. Address the problem: Based on the codes and your mechanical abilities (or lack thereof), you can attempt repairs yourself or take it to a mechanic.
Simply ignoring the check engine light is not recommended, as the underlying problem could worsen and cause more significant (and expensive) damage to your engine.
