* Fuel pressure regulator: This component maintains consistent fuel pressure in the system. If it's failing, pressure might bleed off while the car sits. Pumping the gas pedal primes the system, building pressure to allow the engine to start.
* Fuel pump: A weak fuel pump might not be able to maintain sufficient pressure over time. Again, pumping the pedal helps build pressure to get the engine going.
* Leaking fuel injector(s): While less likely to be the *sole* cause, a slow leak in one or more fuel injectors could gradually decrease fuel pressure in the lines.
* Vacuum leaks: A vacuum leak in the intake manifold or associated lines could affect the fuel delivery system's operation, indirectly contributing to the starting issue.
* Cold start injector: Older cars sometimes have a cold-start injector that helps the engine start when cold. A problem with this injector could require pumping the gas pedal to get enough fuel into the engine. The effect might be more pronounced after a longer sitting period due to the cold engine.
In short: The pumping action temporarily boosts fuel pressure to overcome the pressure loss occurring when the car is idle. This isn't a normal operating condition, and indicates a problem that needs to be addressed before it gets worse.
It's strongly recommended to take your car to a mechanic for diagnosis. They can properly assess the fuel system pressure, check for leaks, and pinpoint the source of the problem. Ignoring this issue could lead to more serious engine problems down the line.
