to pass a smog test

91 c1500 4.3L 170,000

I just passed my smog test, but since the last test my idle 775+/-425 HC ppm reading is up higher than it has been..only 113 ppm (limit is 220).

What repairs can i do to lower the idle HC reading?

My high rmp HC reading (2500+/-300) is reading an awesome 41 ppm compared to limit of 220.

Any fixes to bring down the standing idle HC reading.

ty

Well high HC is unburned fuel or oil. I had the same problem in my 92 1500 5.0L truck. When was the last time it had a full tuneup??? I would look at changing the cap, rotor, plug wires, plugs, PCV , airfilter, fuel filter, and O2 sensor. EGR should be Ok, has to deal more with high NOx emmissions. Thats the route i would go. Best part was replacing all those parts only cost me about 100 bucks. Worst part was that wasnt enough, i had to replace the cat too. ( then again, mine failed really bad)

thanks for the info. Yeah i do full tune ups on mine often. I think it's cat replacement time as well.