I had exactly the same symptons as you last weekend when I replaced my Air flow meter. The Zero position of the plate was not set on the new meter and therefore the idle period between that and the correct basic position was way off, and of course so was the duty cycle. I was seeing fixed readings at X11 pin 3 like you. So I adjusted the zero postion as outlined in the thread below. Zero being the plate at the top edge of the vertical cylinder in the air flow meter and basic being the lambda adjusted to the bottom of the vertical cylinder. When you depress the plate from zero position you can feel the resistance increase when the arm contacts the control plunger. The period between zero and the contact of the control plunger is the idle period. If there is no difference in resistance then it is likely the lambda is well out of adjustment and you need to set the basic position by lowering or leaning out the lambda until resistance is felt at the basic position, the bottom of the vertical cylinder. This at least will get everything set in the right position to begin tuning.
The idle period between zero and basic is max. 2mm. Set at 2mm my car wouldn't start, richened up a bit to about 1.5mm (ish!) I see 50% +/- 10%.
Setting new Airflow Meter - 190 16V
The old airflow meter I replaced also had the same problem, it's zero position was also incorrectly set. If zero is out you cannot set your lamda correctly. If you can't get the correct duty cycle within the idle period spec of 1-2mm you will have to investigate the control plunger seal clearance.
FWIW if the zero position is wildy out of spec (like mine) the idle can surge up and down like it's possesed. If you've also got hesitation under way, it could very well be a stuffed air flow meter potentiometer. Hey, I got lucky, I had the entire kit and kaboodle go west on mine.
In the end it "only" cost me £300 because I was stubborn enough not to go to the dealer. I can really recommend reading the Bosch Fuel Injection & Engine Management by Charles O. Probst. ISBN 0-8376-0300-5