Here are other possibilities to investigate, ranked roughly by likelihood:
High Probability:
* Idle Air Control (IAC) Valve: This valve regulates air flow at idle. A dirty or faulty IAC valve can cause stalling, especially at idle. Cleaning it is a relatively easy and inexpensive first step.
* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation. A failing CKP can lead to intermittent misfires and stalling.
* Throttle Position Sensor (TPS): This sensor informs the computer of the throttle position. A faulty TPS can cause erratic idle and stalling.
* Fuel Pump (or its relay): While the mechanic focused on the sending unit, the *pump* itself could be weak or failing, especially if the car struggles to restart after stalling. A failing fuel pump relay could also mimic this behavior.
* Dirty Fuel Filter: A clogged fuel filter restricts fuel flow, leading to stalling, especially under load (like when stopped at a light).
Medium Probability:
* Ignition System Problems: Worn spark plug wires, bad spark plugs, or a failing ignition coil can cause misfires and stalling.
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's air/fuel mixture, leading to stalling.
Low Probability (but still possible):
* Mass Airflow Sensor (MAF): If equipped, a dirty or faulty MAF sensor can lead to a lean condition, causing stalling.
* Computer (ECU) Problems: While less common, a failing Engine Control Unit could cause a variety of issues, including stalling.
Troubleshooting Steps:
1. Check the basics: Make sure the battery terminals are clean and tight. Check for any obvious vacuum leaks.
2. Clean the IAC valve: This is a simple and inexpensive first step that often solves idling problems.
3. Test the fuel pressure: This will determine if the fuel pump is delivering sufficient pressure.
4. Inspect the fuel filter: It's cheap and easy to replace if dirty.
5. Check spark plug wires and plugs: Look for cracks, corrosion, or excessive wear.
6. Test the CKP and TPS sensors: This typically requires a multimeter or a scan tool.
Recommendation:
Before investing in a fuel sending unit, I strongly urge you to have a qualified mechanic systematically check the more probable causes listed above. Simply replacing the fuel sending unit without addressing other potential issues is unlikely to solve the stalling problem. A thorough diagnostic test is the best way to identify the root cause.
