There is no "idle adjustment mixture" on these cars.

You set the mixture at idle, but it affects all driving. It is adjusted through a hole in the air cleaner with a 3 mm hex key while observing the "on/off" ratio on a dwell meter or DMM. The "on/off" refers to commands being sent to the frequency valve which varies the pressure in the fuel distributor by bleeding off small amounts of fuel into the return line. You want to set the mixture so that the current generated by the O2 sensor tells the little computer to send the "on" signal to the valve about 45% of the time. I believe that "on" closes the valve.

Being able to get a good adjustment and a smooth idle around 650 rpm is one of the basic health indicators of these cars. It means that a s-load of stuff is working correctly.

I have no idea what you did if you stuck a screwdriver in the hole. Maybe you were a little rich or lean and you changed the mixture and fixed it. When you make the adjustment, you need to engage the mixture screw with the hex key and gently push it down to adjust it. If you push too much, the engine will stall.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe