failed a smog check because of high carbon during idle?

Excessive Hydrocarbons are caused by unburnt fuel or insufficient oxygen.

Your problem is not serious because it goes away at fast idle.

Check for vac leaks and anything that may cause a lean mixture as they don't burn properly.

Try opening the plug gaps a little, 5 to 10 thou. The resulting hotter spark will initiate a better burn.

Make sure the intake air is not restricted or contaminated with oil or soot.

Check the timing if it's adjustable

Make sure your exhaust is in good condition and not restricted

What is required for complete combustion?

A Stoichiometric fuel mixture (The O2 sensor should look after this)

An ignition source of the correct type and temperature (In a car it needs to be hot and sustained and arrive at the precise time)

Oxygen

Compression

Correct fuel for the car

Engine must be at the correct operating temperature and not too hot and especially not too cool

No misfire, ignition or mechanical fault

Usually means you're running too rich, I believe. Probably a bad TPS. There are a number of sensors though that send a signal to the PCM to adjust the air/fuel mixture. Could be the IAT sensor or ECT sensor or the MAP sensor or the MAF sensor. No way to know without checking each sensor individually unless you scan it for codes and sometimes it wont throw a code. Get a Hayne's manual and it will walk you through checking each of these sensors.

whilst ever doing emissions attempt constantly run your automobile on the main suitable octane! enable your tank bypass as dry as you are able to and then fill-it-up finished with top classification gas in simple terms for the emissions and run it on top classification for some days earlier the attempt to sparkling out the equipment! additionally verify your tire pressures including approximately 4 psi grants a greater valuable analyzing an intense quantity of less rolling resistance!