Maybe some of you could help me out with this:

KE Jetronic, 124 230E 92, 2.3L
It had low CO readings and HCs were a little high, idle was reasonably smooth but had some vibration when warming up. At that moment the emission readings were:
HC 74 ppm
CO 0,02%

Then, I fixed some small vacuum leaks (idle hoses), changed injectors with seals and O2 sensor (90 kmiles). After that I learned (here) how to measure and adjust the duty cycle:
With battery voltage of 14 volts, voltimeter (at X11 / pins 3 & 2) gave 9 volts (average) at idle, thus the duty cycle was:
(1 - 9 / 14 ) x 100 = 36%.
Turned the mixture screw CCW (leaning), until reading diminished to 7 volts, so duty cycle at idle is now:
(1 - 7 / 14 ) x 100 = 50%.

I did an emission test with the new situation. These are the new numbers at idle:
HC 16 ppm
CO 0,001% (!!, is percent, already multiplied by 100, and it is 20 times lower than before).

Searching I found out that for this car (engine 102) the CO content of the emissions should be in this range:
0,5% - 1,0%.

Considering this, a 0,001% of CO though is good for pollution, it is far from how the system was designed. In addition, idle becomes smoother but is still a bit shaky when T° is raising and near 60°C (I suspect when the O2 sensor activates and the ECU's mixture corrections begins).

Could all this be indicating that there is still a small vacuum leak?
Please give me some light about what's going on here.

Thanks in advance for any idea.