I have never adjusted the steering ger box on 123's with the engine running. After the adjustment, I always check with the engine and PS working.
I read somewhere that the wheels should also be off the ground, but I don't know if that is true or not.
Be careful not to over adjust (counter-clockwise) the adjuster too far or you can dent the recirculating balls? I believe this is what happens.
Free play, steering wheel centered, is I believe 25mm.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)