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

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1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
Sold:
1987 VW Jetta GLE 16V, Recaro seats
1982 Volvo 240 DL (lovely car!)
and few more american cars.

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.
How to adjust idle speed on OM603?

__________________
1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
Sold:
1987 VW Jetta GLE 16V, Recaro seats
1982 Volvo 240 DL (lovely car!)
and few more american cars.