I have a 2002 SE with the SPI motor.
I have been driving with the cel on. I plugged in a obd2 code reader and found out the rear o2 sensor was bad. I also just replaced the pvc elbow due to a split in it causing a leak and giving me a rough idle. After replacing the split elbow i have taken notice of my cel off and other times back on. Can this be related in any way or is it just actually a bad o2 sensor? I am new to the Focus world and plan to do more to also give me some more ponies under the hood. Any and all help/ advice would be appreciated. Thanks