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.