Oxygen Sensor

Does the oxygen sensor effect the HC emissions output on a 91 4-cyl Camry?

it could, but you better check the PCV valve first. Its probably clogged and not releasing waste products as it should. Very cheap fix.

What were your other readings? You need to compare all the gases to try and pinpoint the problem.

Ok Pedro heres the rundown...When I first had the car tested it was fine expect for NOx..I did all the work on the car that you helped me with..Plugs, wires, coil,dist. cap, rotor and EGR valve, I went back for retest and all was good except for the HC.  It went from running lean to running rich. The HC went from 0.13 g/mi to 1.85 g/mi.

I was told that the 91 4-cyl Camry has no PVC valve

It has P(ositive)C(rankcase)V(entilation) but probably not a poppet valve. It probably has a venturi that does the same job, although I don't think as well, as a PCV valve. A PCV valve makes sure you don't get a pressurized crankcase. My understanding is negative crankcase pressure is better. It sucks into the engine intake and will draw any gases from the crankcase, including by-pass gases that could be extra HCs. You should try to locate the venturi. Look for a vacuum hose on the intake around the location of the butterfly valve that runs from a valve cover. There may also be a separate breather hose from a valve cover but that will have a larger diameter hose. I doubt it is blocked, but can't hurt to check it and maybe blow some carb cleaner through it.
 
I would go back to bacics. Check your compression, maybe even do a leak down test if the compression is not up to snuff. HC is unburnt fuel. If you have an exhaust valve or two that is not sealing then on compression they will blow raw fuel into the exhaust. If your rings are bad that will blow raw fuel into the crankcase and be sucked up through the PCV. How do the plugs look? Do they look like a rich ratio? Do they look like you're burning oil? Have you changed the oil? If you are getting bypass in the piston rings then fuel will accumulate in the oil, that could up your HC readings. An oil analysis on the old oil will tell you if you have excess fuel in the oil. But do the compression test first.
 
Are you under the gun for emissions? Are you allowed only a couple of tests before you have to take different ($) action. Are the tests free after the first one from you local station? Is a garage doing the testing or a government facility? The only reason I'm asking is for a determination of the problem. If you do a bunch of stuff then who's to say what was the cause. It would be nice to do one thing and then get it tested.  

Sometimes an Oxygen sensor can be the culprit but it depends on how the 02 sensor is failing. Usually when an 02 sensor fails it causes the computer to make the engine run with a richer mixture which in turn would cause your HC emissions to be higher.  I have also seen where a bad 02 sensor will cause a lean condition increasing CO gasses