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!