Toyota Repair: Emissions Failure CO, air fuel mixture, o2 sensor

Question
My 92 Previa 2wd just failed the CO part of the inspection test.  What should be replaced? The van has 190,000 miles.

Answer
High CO means that the air/fuel mixture is too rich, too much fuel/not enough air, there could be many causes for this ranging from a simple solution like a clogged air filter, a leaking fuel injector, a leaking cold start injector, a bad O2 sensor, by the way is the check engine light on?