My 1992 VG engine car runs well but just barely passed HC emissions in Pennsylvania. The car tested 273 with a limit of 275. Car has 115000 miles and all emissions controls are original. Wires, dist cap, spark plugs have all recently been changed. What causes high HC and what is most likely going bad?

 

Cat / o2
dump a bottle of rubbing alcohol in the tank and go back through.

 

Is that number at idle or high speed? I would check the operation of the EGR valve.

 

Test RPM was at 1717 rpm's

 

I dont think the egr opens at that rpm, I think it has to be at least 2000rpm.
But definitly the EGR can get a lot of carbon build up, and then the vavle won't close properly, and that can lead to a poor idle. I actually cleaned mine out, it really didnt look that bad in the first place but I did it anyway.

Another cause for you high HC, could be your injectors, one or more of the o-rings are probably leaking.

If the problem were mainly the cat. then I'd suggest getting a bottle of the liquid sea-foam (the same results can probably be achieved by using spray carb cleaner). I'd suggest you didnt put the sea-foam in the gas tank or in the oil, just use it for the intake manifold and let it suck it in (but do it very slowly).

And as suggested before, if you have not done your 02 sensor, then do it. You'll get better fuel economy.

 

EGR has a lot more to do with NOx than HC levels

 

My first step would be to check the EGR valve.
Everything that I know from engines lead me to that direction.

 

and apparently for emissions it's not much.
HC is unburnt fuel your EGR has little to do with unburnt fuel.
As previously stated Fuel injector leaking or faulty o2 are more than likely culprits

 

If the oil hasn't been changed, do that also.

 

Doh forgot about that too