Black smoke(carbon residues) and strong gasoline smell!

I drive my Discovery 1-1996, 4.0 liters with manual trans. everyday. But during the las three weeks she start to have a problem with the motor revolutions. Every time I have to stop, she drop the revolutions to 0 rpm and turn off the motor. I went to a LR specialist and they notice the air control idle was not working, so they substitute and reset with the T4 software. But the problem continue, but the rpms; its do not drop to zero; only to 200rpm and increase to 800rpm and is a heavey smell of gasoline in the exhaust and the muffler tip have a lot of carbon deposit and the smoke is dark to black. I change the spark plugs and clean the KN air filter. The old sparks plugs was with a lot of carbon deposit in the tips. Im worry to damage the O2 sensors, if its already are gone. Anyone can give a hint. Thank you!

If you are using a K&N, I would also clean the MAF Sensor.

Depending on mileage and if you have fuel injection or a carb, it could be the injectors starting to go. Have them cleaned, if that doesn't work, you may need to look into replacements.

Have you changed the fuel filter?

could be injectors ro maybe the fuel pressure regulator. I had a Ford Explorer that did this and it was casued by the pressure regulator failure. It was giving full pressure to the injectors and over fueling like a monster.

Yes Joey, when I change the fuel pump year ago the shop change the filter also. Because I use my disco for a daily drive, when I clean the filter, I always clean the MAF with a CRC product and WD40.

WD40 will ruin a MAF sensor as it leaves a nasty residue.

Check for a cracked vacuum line at the fuel pressure regulator just in case.

Drivers side back of intake small roundish thing with a vacuum line attached.

I did not know about the WD40, I will stop the practice. As soon as I arrive to my home I will check all the vaccum lines. Thanks again.

deleted by poster - irrelevant
:confused:

Finally I found the problem the problem that make the T4 software, reads misfire codes, O2 sensors and another one. With a good light, a lot of patience and a dark beer, I was checking one by one of the sensors in the gem motor. Late night, I move one of the injector plug and the gasoline temperature sensor fall down. I tried a lot of time to put it back and I noticed was totally crack and in the past was installed back with a heavy load of glue! Every time I hold the sensor with against the couplig , the computer make a goood reading and the black smoke stop. I read that the sensor send a signal to the trottle and clos it, when is working, but when it dont work the trottle still open and the mixture is really heavy in gasoline. Now, start to cut cables and install another plug! Thanks everyone!!

Dang, glad to hear you found the issue and sorry I wasn't much help for that one... can't account for prior re-engineered parts.