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!!

That car is not quite the same as my car. However, symptoms like that are often caused by vacuum leaks. Vacuum leaks are often caused by:

A small vacuum hose got disconnected when someone was working on the car.

A hose got brittle and now is leaking and/or cracked.

Have you tried searching on W202 idle surge etc?

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra