2002 mercedes benz clk 430 convertable

You may have a closed or gummed up injector issue. You also may have a catalitic converter going bad. You also should check your oil and see if the oil is a cream color which means you may have water entering the engine chambers due to a bad gasket or cracked head. That may require a pressure check of all the cylinders. My first check would be the injectors. Then the timing/ignition system. Do you get any signals on the dash giving you a check engine with codes? Then again you may have gotten a shot of bad fuel and may have water or dirt in it plugging up your fuel system.