* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation. A faulty CKP sensor can cause erratic engine behavior, including hesitation, stalling, and the ability to restart immediately (as the sensor might be working intermittently). This is a very common cause of these symptoms in older Foci.
* Cam Position Sensor (CMP): Similar to the CKP, a faulty CMP sensor provides incorrect information about the camshaft's position, leading to misfiring and stalling. Again, intermittent failure explains the ability to restart.
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor provides inaccurate readings, leading to a lean or rich fuel mixture, causing hesitation and stalling.
* Throttle Position Sensor (TPS): If the TPS is malfunctioning, the engine computer might receive incorrect information about the throttle position, leading to inconsistent fuel delivery and stalling.
* Fuel Pump: A weakening fuel pump might not be supplying enough fuel under higher demands (acceleration), leading to hesitation and stalling. If the pump is weak but not completely failed, it can recover enough to allow a restart.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to similar symptoms as a weak fuel pump.
* Ignition Coil(s) or Spark Plugs/Wires: Intermittent ignition problems (failing coil, worn spark plug, or bad wire) can cause misfires, leading to hesitation and stalling. Again, the intermittent nature explains the easy restart.
* PCV Valve: A clogged Positive Crankcase Ventilation valve can lead to excessive crankcase pressure, affecting engine performance and potentially causing stalling. This is less likely to be the *primary* cause of this specific symptom set, but it's worth considering.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any stored trouble codes. This is the quickest way to narrow down the possibilities. Many auto parts stores will scan your car for free.
2. Inspect the obvious: Check the fuel cap for tightness (a loose cap can trigger a code related to the fuel system) and visually inspect the visible parts of the ignition system (wires, plugs – if accessible).
3. Consider the age of components: Parts like the fuel filter, spark plugs, and ignition components are wear items and should be replaced periodically. Given the age of the car, these are prime suspects.
4. Professional Diagnosis: If you're not comfortable diagnosing the problem yourself, take it to a mechanic. They have the tools and expertise to accurately diagnose the issue.
It's crucial to diagnose the problem correctly before replacing parts. Replacing parts randomly can be expensive and ineffective. The DTCs from an OBD-II scanner will provide the best starting point for your investigation.
