Emissions test tune-up

[Meridivs]

It's time for the periodic emission-test for my '92 Pontiac Trans Sport.

The engine is a 3.1 TBI V6 and it's idling a little rough. Acceleration and idling with AC ON is fine but idling with no load is not ok.

I have done so far:
- plugs & spark wires
- new air filter
- new distributor cap and rotor
- new Ignition Control Module
- cleaned-up EGR
- new PCV valve
- new thermostat (I don't know if it's related)
- new injectors

The car was idling this way since I got it and nothing I did changed anything. Except turning on the AC which increases the engine idle speed at ~1000rpm, then it idles fine.

Do you have an idea what else I can do to improve my emissions (they check it here at idle rpm)?

Any advice, things I might look into are very much appreciated!