Please try a search on "lambda" or "duty cycle" or "on-off ratio" or closed loop." There are numerous posts on how to adjust the mixture. It's one of the most discussed problems on the 380's.

Basically, when the engine is warm and in closed loop, an analog computer is reading air-fuel mixture data in the exhaust stream from the oxygen sensor. The computer signals the frequency valve to open or close to lean or richen the mixture. The ideal mixture setting is when the computer sends a 50% "duty cycle" to the valve. That means that the mixture is set at a point where the computer can maintain ideal combustion by keeping the valve open 50% of the time. This is what you measure with your meter at pin 3 of the diagnostic socket. And you adjust the mixture to obtain the 50% reading.

But for this to work, you need a good oxygen sensor, a good fuel distributor, injectors working right, tight injector seals, and good vacuum. You cannot make up for any of these by twisting the mixture screw.

You cannot treat this car like it has a carburetor. The K-Jet injection is very straightforward, once you understand its principles. There is a reasonable explanation of how it works on Wikipedia and other web sites, as well as numerous books and manuals. If you don't have a basic understanding of how the system works, you should not be messing with it or asking this forum for advice.

__________________
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