EZL round timing switch question (Euro)
 

My car has got 2 same looking round adjusters
First one is EZL KAT adjust. It is located nearby the fusebox and has 3,N,4,S green letters written on it. I read that this adjuster is for setting the fuel octane (timing retard). S means super, N is for regular.
My question is, what is the other same looking EZL adjust located behind the battery used for? It has letters 1 to 7 written on it in white color. The part number is 545 71 28. I am attaching its picture.
My car 1989 230E, 4 cyl, 8 valve
Hurshi

found the answer
 

That second adjuster is called a resistance trimming plug. It is used for adjusting the idle speed. Position 1 is for setting it to 600 rpm, position 7 is for 740 rpm. The rest of the position are in the following link.
http://www.peachparts.com/shopforum/diesel-discussion/41143-how-adjust-idle-speed-om603.html?highlight=resistance+trimming+plug