Toyota Repair: T-100 failed emissions test, air fuel mixture, air leak

Question
My 1995 T-100 V-6 153k miles failed emissions CO was too high - 266ppm. What would be the most likely reason?  

Answer
High CO means that the engine's air/fuel mixture is too rich, it's getting too much fuel compared to air.
There could be an intake air leak causing the computer to make the A/F ratio rich, in any case there should be a check engine light on, is there? If so I need to know the trouble code.