* Worn or damaged spark plug wires: Moisture can penetrate cracks or worn insulation on the spark plug wires, leading to misfires and sputtering. The high voltage needed for ignition can arc across the wet insulation instead of jumping the gap in the spark plug.
* Wet distributor cap and rotor (older vehicles): Similar to spark plug wires, moisture in the distributor cap and rotor can cause arcing and misfires, resulting in sputtering. This is less of a problem in modern vehicles which generally don't use distributors.
* Leaking fuel injectors: While less directly related to rain, a leak in a fuel injector can allow fuel to accumulate and then mix with rainwater, potentially disrupting the fuel-air mixture and causing sputtering.
* Ignition coil problems: A failing ignition coil can be more susceptible to moisture, leading to inconsistent spark delivery and sputtering, especially in wet conditions.
* Air intake leak: Water can get sucked into the air intake through a leak, disrupting the air-fuel mixture and causing the engine to sputter.
* Short circuit in the wiring harness: Water can cause short circuits in the electrical system, leading to various engine problems, including sputtering. This is less common but a significant possibility.
* Water in the fuel: Although less likely in modern vehicles with well-sealed fuel systems, water can still enter the fuel tank, potentially causing problems.
In short: The rain isn't directly *causing* the sputtering, but it's exposing pre-existing weaknesses in the car's electrical or fuel systems. The sputtering is a symptom, not the disease. You need to have a mechanic diagnose the underlying problem.
