Reminds me of my Graphite at 90,000 miles. O2 codes and misfire codes anytime I got into it.
Put 12 plugs and 12 plug wires on it - fixed. And it ran WAY better, I"d not realized how bad the car was running until I put those parts in it.

But it SOUNDS like you just bought it, is that right? If so, there is no telling what is going on. The fuel could be separated, or even varnished, if the car sat a long time.
The fuel filter/regulator could be at wit's end...
The MAF could be filthy...

If it were me, I"d take advantage of the fact that Arkansas will be seeing some GOOD weather this weekend - change plugs and plug wires (it is TIME) and run some gas thru it this weekend.
Likely, that alone will do it. Order plugs and wires TODAY - search "2003 Mercedes SLK320" and you will pay less than if you search "Crossfire".