Intermitent problem with engine stopping at low RPM's and car failing to start
 

I have a 2009 CLK350 with 120,000 KM and I've been having issues with the engine stopping at low RPM's, I haven't had this issue at higher RPM's greater than 2000. When the engine dies the dashboard lights up, and the RPM drops to 0, but the electrical systems are still functioning.

Another issue that may be related is occasionally the car fails to start. I'll insert the key, and turn to start, the accessories turn on fine, but the car fails to crank. I'll turn off the vehicle and remove the key and reinsert, and it'll eventually work.

I've changed the spark plugs, and the crank position sensor, and engine thermostat, performed a transmission service, installed a new starter relay, but none of these things have seemed to help. When the car is running it operates normally.

I'm not really sure what to troubleshoot next.

I could be that your battery is dying, Check that the voltage is 12.5V when the ignition is off, 11+ V when cranking and 14+ V idling just after a start.

Welcome to the forum!

I'd pull codes. Even if the MIL is not illuminated, there might be some stored DTCs.