Here's a breakdown of the likely culprits, ordered from most to least likely:
* Fuel Injectors: This is the most probable cause given the symptoms. Clogged or leaking fuel injectors will deliver an inconsistent fuel spray, leading to a rough idle, sputtering, and a rich mixture (black soot). The fact it's worse under load (in gear) reinforces this. A leaking injector can also lead to increased fuel consumption and eventually, the smoking exhaust.
* Fuel Pressure Regulator: This regulator controls fuel pressure in the fuel rail. A faulty regulator could be delivering too much fuel pressure, leading to the rich condition.
* Mass Airflow Sensor (MAF) Sensor: A faulty MAF sensor provides inaccurate readings of the air intake, causing the computer to compensate by injecting too much fuel. This is less likely given the consistent black soot (consistent rich condition), but it's still a possibility.
* Throttle Position Sensor (TPS): A malfunctioning TPS provides incorrect information to the computer about the throttle position, affecting fuel delivery and idle. This is less likely to cause *only* black soot, but could contribute to the overall problem.
* Intake Air Leak: A leak in the intake system (hoses, gaskets) will introduce unmetered air, upsetting the air/fuel mixture. This could lean out the mixture at times and enrich it at other times, making diagnosis more challenging. A very large leak could be causing the rich condition if it is after the MAF Sensor.
* Catalytic Converter: While you've mentioned the smoke, a clogged catalytic converter is unlikely to *cause* the rich condition. The black soot indicates the problem is upstream (before the cat). However, a clogged cat *could* be exacerbating the issue and contributing to the smoke.
Troubleshooting Steps:
1. Fuel Pressure Test: This is crucial. A qualified mechanic should check the fuel pressure to see if it's within specifications.
2. Fuel Injector Cleaning/Testing: This is highly recommended. Either a professional cleaning or replacement might be needed.
3. Fuel Pressure Regulator Test: Check its operation to ensure it's regulating pressure correctly.
4. MAF Sensor Inspection/Cleaning: Inspect the MAF sensor for dirt or damage. Clean it carefully with MAF sensor cleaner (following instructions precisely), and if that doesn't help, replace it.
5. TPS Test: Verify the TPS's voltage output using a multimeter.
6. Vacuum Leak Check: Carefully inspect all vacuum hoses and connections for leaks. Use a vacuum gauge to verify proper vacuum readings.
Important Note: Continue driving with a severely rich mixture is detrimental to the catalytic converter and could permanently damage it. The excessive fuel can also wash away lubricating oil from cylinder walls, potentially leading to engine damage. Get this diagnosed and repaired promptly by a qualified mechanic. A fuel system analysis will be very beneficial in pinpointing the precise problem.
