Pulled codes...what do they mean?

[PKRWUD]

Code 67 is because you didn't hold the clutch pedal to the floor during the test. If you did, then it could be because of a problem with your a/c circuit, or because the a/c was on during testing. More than likely, you didn't hold the clutch pedal to the floor during testing.

Code 31 means there's a problem with your EGR valve, or more specifically, the sensor that measures it. Disconnect the harness at the EVP sensor, and jump the brown/green wire and the orange/white wire. Run KOEO self test again, and look for a code 35. Ignore all other codes. If a code 35 comes up, replace the EVP sensor.

Code 66 means there's trouble with the MAF. It usually happens because someone unplugs the hose that goes to the oil fill tube from the TB, or because of a loose clamp holding the MAF, or the tubes, in place. Inspect them all and make sure it completely sealed. Next, inspect the electrical connector to the MAF, and make sure it's clean and tight.

Code 96 means your fuel pump relay is on it's way out, or the power wire to it has a bad connection. I would replace the relay, and inspect the wires.

Take care,
~Chris