Hi, i have a '96 W202 C280. After starting the engine and when the engine begins to get hot, the idle goes up and down. The engine is revving on its own. The idle becomes worse when the engine is hot, and a black smoke will come out from the exhaust. There is no check engine light yet on the intsrument cluster. Sometimes the engine will stall. I have replaced the fuel filter, cleaned the throttle body yet the problem remains. Help!!