92 voyager emmisions problem?

i have a 92 voyager with 3.0 motor, two wheel drive auto trans, problem i have is high hydro carbons that is failing emmisions. no engine codes in computer, i have replaced idle speed motor, throttle position sensor, fuel filter, plugs wires cap rotor timed the motor and also ran seafoem through throttle body, added lucus injector cleaner and am now at a loss. no rotten egg smell in exhoust so i do believe cat is ok. only problem can tell is little rough idling! gas milage is good, acceleration is good. van has 136000 miles on it. any ideas it is boggling me!!

Dirty engine oil is full of hydrocarbons. If you haven't already, try changing the oil and filter and the PCV valve.

Do you also have high NOX? High nox would be an indication that the EGR system isn't working. It also does also cause high(er) hydrocarbons and rougher idling.

A high HC failure only indicates a bad catalytic converter. Pull the old one and take a look.

Fisrt thing I would've replaced was the O2 sensor...

Read through this. Gives you an idea of what to look at for hydrocarbon failures. http://www.advanceautoparts.com/english/youcan/html/ccr/ccr20040701s2.html