* Throttle Position Sensor (TPS): A faulty TPS might be sending incorrect signals to the ECM. The ECM might be interpreting this as a need for more fuel to start, hence requiring the gas pedal input.
* Crankshaft Position Sensor (CKP): A malfunctioning CKP won't accurately tell the ECM the engine's position, potentially leading to a fuel delivery issue during the starting sequence. The ECM might compensate by only allowing fuel when the gas pedal is depressed (providing some engine feedback).
* Mass Airflow Sensor (MAF): A problem with the MAF sensor can cause the ECM to misinterpret air intake, affecting the fuel-air mixture calculation. Pressing the gas pedal might trick the system into providing a more workable mixture.
* Fuel Pump Relay: While less likely to be directly related to only starting with the gas pedal depressed, a failing relay might cause intermittent fuel pump function. Depressing the pedal could sometimes temporarily improve the circuit.
* ECM/PCM Issue: The engine control module itself could be malfunctioning, leading to unusual starting behaviors. This is a more serious and potentially costly problem.
* Security System Issue: In some vehicles, a security or immobilizer system issue can prevent starting. While less common to only start with the pedal depressed, it's worth considering. This is more likely to manifest as a complete no-start.
What to do:
1. Check the obvious: Ensure the battery is fully charged and connections are clean and tight.
2. Check engine codes: Use an OBD-II scanner to retrieve any diagnostic trouble codes (DTCs). These codes will provide valuable clues about the problem.
3. Professional Diagnosis: Given the complexity, it's strongly recommended to take your vehicle to a qualified mechanic for a proper diagnosis and repair. Attempting to fix this without the proper tools and knowledge could lead to further damage.
Do NOT continue driving the car if it is exhibiting this issue. The underlying problem could worsen and cause significant damage to your engine.
