Try holding the engine RPM's to approximately 2000 and make an incremental adjustment to your CO while monitoring your meter. The adjustment should bring your EHA current within the desired control range of 0mA. This may help reduce some of your HC; however, it is unlikely to have any significant effect to your NoX.

The 1990 103 should be fitted with an EGR system, the purpose is too assist with a good portion of NoX reduction. Your tube may be partially restricted due to carbon build up at the intake manifold opening. A completely clear tube will help reduce the NoX to some degree (case by case basis), final reduction is addressed by the CAT.

CAT temp is critical, as well it needs to working to some level of efficiency and your's may be getting tired.

Just say no to "Carbecues," repair the fuel leak.