Toyota Repair: 90 Camry cant pass emissions, air fuel mixture, hydrocarbon emissions

Question
I bought a '90 Camry V6 LE Sedan from my brother because he gave up not being able to pass an emissions test. He spent a few thousand on repairs. Nearly everything is new .. Cat converter (twice), oxygen sensors, ERG valve, and the list goes on. I tested the car (after stored for 2 years) and it failed the HC test. From what I've read, this is usually a mis-fire issue, but this car runs perfectly - new wires, cap, plugs, PCV, vacuum lines, etc. I don't want to repeat the same costs as him. Other owners of this SAME car tell me they can't pass either. Is this related to defective parts on this model, like the computer? I have no idea what to do because most everything has been done once or twice. Any suggestions as to lowering (at least temporary) the Hydrocarbons - i.e. different plugs, fuel treatment, anything? Thanks for your help!!!

Answer
You are correct, high HC emissions are normally due to a misfire but can be caused by other conditions, higher than normal HC is caused by inclomplete combustion, the engine is not burning all of the fuel it takes in, some of the unburned fuel is getting into the exhaust and shows up as hydrocarbon emissions that are too high.  
Causes for this could be a cylinder that has a loss of compression, a headgasket leak or an intake air leak, these problems will make the computer try to compensate for the extra air and make the air/fuel mixture richer, in turn the engine can not use the extra fuel and passes it through the exhaust. I don't know what other repairs were made before that cost thousands of dollars you weren't specific on that, for some reason the engine is not operating at it's optimum and the reason why needs to be determined, I would suggest having the engine cylinder compression tested and then have them do either a chemical block test or check for hydrocarbon emissions in the cooling system, this can be done with an emission analizer. If the HC readings are very close to the maximum you may be able to use the best fuel you can get and add an octane booster to the gas before doing the next emissions test, it may just work to squeeze by.