If there was no cat, the answer would be to lean out the idle and idle. A little readjustment of the idle mixture screws and maybe the throttle opening (idle speed). But the cat is also a possibility and to a lesser degree the EGR.

IIRC, the early catalytic converters were mainly to reduce the NOx. The other emmissions were controlled by running higher idle temperature (leaner, combined with an idle stop solenoid so it won't diesel on shut down). Your '93 probably came with a 3-way cat which was designed to help reduce all the bad stuff, but again IIRC NOx reduction is the main job of the cat.


So, if you fiddle with the idle-off idle, bring them to the specs on the hood sticker (if that's option on a '93) that could squeak it by.

The EGR valve operation should be testable with a vacuum gage and pump. If the EGR exhaust gas passages are partly plugged up - that's harder to do anything about. You can access the valve orifice but thats about it without a teardown. EGR systems usually have temperature and vacuum switches Off the top of my head there is no EGR until coolant reaches a certain temperatures, no EGR at WOT, etc.


If you want to read more about diagnosing exhaust for relatively modern cars there was a Toyota (ASE?) pdf online in various locations. This may be it here:
http://www.readbag.com/autoshop101-forms-h56