You might check to see if you have vacuum at the fuel pressure regulator:
http://www.4crawler.com/4x4/CheapTricks/22RE_Engine_Pix/8.html

With no vacuum feedback, the fuel pressure can rise too high at low engine loads and cause the engine to run rich (high HC readings).

And yes, you could test the coolant temp sensor, if it is reading too cold, the ECU will try to get the engine to warm up by dumping in extra fuel.

r.c.brown@ieee.org
TruckEditor@tlca.org
Project: 4Crawler
4Crawler OffRoad - 4x4Wire discount code