1990 190e 2.6 Lambda Screw Reversed?
 

On mine, when I turn the screw CCW my % decreases. At 2500 rpm the % decreases by 10%. This is opposite of everything I've read?

With a duty cycle of 55% at idle, the pedal feels sluggish. If I bump it up to 60%, I get a much better take off from idle. Again, opposite from what I've read.

meter in correctly?

I think I figured it out.

http://www.peachparts.com/shopforum/tech-help/161055-sears-multimeter-82139-duty-cycle-check.html

I am also using a sears meter. I swapped the leads (red in pin 2, black in pin 3). Now I get 47% at idle and 52% at 2500 rpm. Although the readings are a little wild at 2500 rpm. It can go as low as 47% and as high as 55%.