* Flooded Engine: The most immediate possibility is that your engine is flooded with fuel. This can happen due to a malfunctioning fuel injector, a faulty fuel pressure regulator, a sticking or faulty throttle position sensor, or even a problem with the fuel pump delivering too much fuel. The excess fuel isn't being burned properly at idle, leading to sputtering, and when you rev the engine, some of the unburnt fuel is expelled through the exhaust.
* Faulty Fuel Injector(s): One or more fuel injectors might be stuck open or delivering excessive fuel. This would lead to a rich fuel mixture, causing the sputtering and unburnt fuel in the exhaust.
* Fuel Pressure Regulator Failure: A faulty fuel pressure regulator might not be regulating fuel pressure correctly, leading to excessive fuel pressure in the system. This would cause the same symptoms.
* Throttle Position Sensor (TPS) Problem: A faulty TPS can provide incorrect information to the engine control unit (ECU), leading to an excessively rich fuel mixture.
* Mass Airflow Sensor (MAF) Problem: A malfunctioning MAF sensor might provide incorrect information about the amount of air entering the engine, resulting in a too-rich fuel mixture.
* Air Intake Leak: While less likely to cause raw fuel in the exhaust, a large leak in the air intake system could drastically alter the air/fuel ratio, leading to a rich mixture and similar symptoms.
What NOT to do: Keep cranking the engine repeatedly trying to get it started if you suspect a flooded engine. This will only make things worse.
What to do:
1. Stop driving immediately: Continue driving could damage your catalytic converter.
2. Don't try to repeatedly start the engine: This could make the flooding worse.
3. Have it towed to a mechanic: This is not a DIY problem. The fuel system requires specialized tools and diagnostic equipment to pinpoint the exact cause. Trying to fix it yourself risks further damage or injury.
The raw fuel in the exhaust is a strong indication of a serious problem that needs professional attention. Ignoring it could lead to significant engine damage or even a fire.
