Just a few additional thoughts on this:
I would check the cap and rotor if that hasn't been changed lately. They can definitely cause a misfire condition if the contacts are burned. They really should be changed about every 30K based on my experience with other Bosch distributors on my VWs and Volvos in the past.
If your oxygen sensor is old, you might want to change that as well - perhaps the duty cycle isn't refreshing as quickly as it should anymore thereby causing higher emissions.
As mentioned earlier, is your catalytic converter in good shape?
On the LH 2.2 Jetronic injection: This system is TOTALLY different from the CIS system and does not have an idle mixture screw (as far as I know - unless it is part of the MAF.) LH 2.2 uses an electronic mass airflow meter (MAF) like most other cars these days, and the computer adjusts the idle mixture based on feedback from the oxygen sensor, etc.
I have also heard that filling up the tank with Super Unleaded (higher alcohol content as mentioned earlier in this thread) and taking a hard run down the highway right before an emissions test can help with the numbers as well.
I hope you find a solution soon!
Andrew S.