M103 (euro 300s) spark plugs are supposed to be replaced at 12k miles intervals. Yours are gapped correctly aren't they?
The air filter is clean isn't it?

The euro 300 I kept in Blighty (208k miles and original injectors, but no cat) passed its UK emissions test at 184 ppm HC and 0.134% CO, although it must be subject to a higher limit than yours. The CO is way too low, but was set by the test station. The HC didn't alter much though.
Presumably, your car passed its emissions previously, so, have you changed or had anything done to it since?