The screw is how you change the mixture.

The EHA current (the electronic control system), the duty cycle (electronic control system) or CO in the exhaust is how you measure the mixture to get the correct setting. It cannot be set "by ear" on these cars with any real success.

Just like ignition timing -- you turn the distributor to change the setting, but you use a timing light and the scale on the crank pulley to get the corret setting.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!