co and hc go hand in hand with engine efficency, full and complete combustion, what he could have done was try to run it in a lower gear, reving it higher to further burn unburnt fuels, but this would increase NOx and if it was close on that it might have made you fail, but ya smoke em is right, when your doing the test it starts at 90sec, if it doesnt move you to the next test by 68sec you usually are going to fail, but if its close and runs through the whole test it will give you a "second chance" to see if its gonna pass...