Electrical Issues:
* Faulty Alternator: While a failing alternator *can* trigger the check engine light, sometimes the issue manifests as intermittent power loss before the light comes on. A failing alternator can't keep the battery charged, leading to stalling.
* Bad Battery Connections: Corroded or loose battery terminals can interrupt the electrical flow, causing intermittent power loss. Clean and tighten them first – this is a simple, cheap check.
* Wiring Problems: A short circuit or broken wire in the ignition system, fuel injection system, or other critical circuits can cause intermittent power loss. This is more difficult to diagnose and may require a professional.
* Crankshaft Position Sensor (CKP) or Cam Position Sensor (CMP): These sensors are critical for engine timing. A failing sensor might cause intermittent stalling without triggering a code, especially if the failure is intermittent.
* Ignition Switch: A worn or failing ignition switch might not consistently supply power to the engine.
Fuel System Issues:
* Fuel Pump: A failing fuel pump might not always deliver enough fuel, leading to stalling or loss of power. It may only be intermittent before it completely fails.
* Fuel Filter: A clogged fuel filter can restrict fuel flow, but usually doesn't trigger a check engine light unless the blockage is severe.
* Fuel Pressure Regulator: A malfunctioning fuel pressure regulator can lead to inconsistent fuel pressure, causing power loss or stalling.
Other Possible Causes:
* Vacuum Leaks: A leak in the vacuum system can disrupt engine performance.
* Throttle Position Sensor (TPS): A faulty TPS provides incorrect information to the engine control unit (ECU), possibly causing stalling or power loss. While often throwing a code, it's not always guaranteed.
What to Do:
1. Check Battery Terminals: Start with the easiest and cheapest fix – clean and tighten your battery terminals.
2. Have the Car Scanned: Even if the check engine light isn't on, a professional mechanic can use a scan tool to check for any pending or stored codes (some codes are "pending" before they trigger the light).
3. Consult a Mechanic: Given the intermittent nature of the problem and lack of a check engine light, a professional diagnosis is highly recommended. They have the tools and experience to pinpoint the exact cause.
Ignoring the problem could lead to more serious damage or a complete breakdown. It's best to address this issue promptly.
