The engine may develop a stalling and/or no start condition due to a failed crankshaft position sensor.Google+
Car Problem Reports
Mercedes-Benz CLK550 Engine Performance Problems Due to Crankshaft Position Sensor Failure
Mercedes-Benz CLK550 Problem
Visitor, 2008 Mercedes-Benz CLK550, 50,000 mi
Engine tunrs off on occasion but more often, it will surge at idle from approx 750 RPM to 1800RPM instantaneously and unsexpectedly, causing the car to jump. Very dangerous problem if your foot is not already on the brake pedal and expecting it.