I can start my car no problem but it wont accelerate at all I can only drive 5 miles per hour, after checking the k40 relay there is a burn mark on the circuit, I wonder if this cause all the trouble, does anyone has similar problem? please help me out thanks.
1999 Mercedes slk 230

 

In my case (check my old posts) the k40 relay will cause stalls & non starting
so not sure - but you could ask your dealer to install a new one to cure or eliminate ?