Similar to what I have a while back. I did the following just to find out what happened:
- I replaced the fuel filter. It was dirty to begin with, so worth changing. Location of it is underneath the car, right in front of gas tank (do search on replacement of fuel filter).
- I cleaned the MAF w/ cleaner.
- Have AutoZone to read engine code (free), good way to find error code.
- Do search on crank sensor here, maybe related (not sure).
- Finally, I found out from dealer that it's a bad K40 module. Part is about $140 or you maybe able to fix it (do search on K40 relay).
This car is very easy to work with and you'll find good resources here to troubleshoot it. I drive the SLK more & harder now after that K40 replace and enjoying every bit of it
Someone may have different input about your SLK.