Code question

Hard to say - but it makes sense to be sure the electrical system is charging correctly before trying to diagnose the issue. What kind of shape is the battery in ?

I'd take it to Autozone or PepBoys and have them wheel their battery/alt. test cart out and do a load test on both. I wouldn't chase the codes until you've got the electrical issue figured out - no telling how improper charging is throwing other things out of whack.

CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Check for the same results on pin 27 on the computer.