I have just recently installed long tube headers on my 2000 Chevy Silverado I still have the EGR valve hooked to the header but a vacuum line and another egr looking peice for smog I pulled apart not thinking that would cause a problem, the truck is throwing no codes but is missfiring, all cylinders are firing off and each header pipe is warm but it had a rough idle and drives like crap, the o2 sensors are pluged in and everything but could anybody give me some strong info?

 

When were the O2's replaced? Is the MAF plugged in. You can try spraying some water (Spray bottle, not garden hose) around the intake to see if it changes idle. That can grab a vacuum leak.

 

Check spark plug wires. Make sure none of them touched and burned through. And also that you put them on all the way

 

Torched wire for sure.

 

Cracked plug(s) from header installation

OR

Unmetered air from "vacuum line and another egr looking peice for smog I pulled apart not thinking that would cause a problem"

 

Could a bad o2 sensor cause a missfire?

 

It could. Or it could just be giving a bad reading I think.

Did you check all the wires/plugs?

 

Cracked plug happened to me when my LTs where put on - take each one out and check the porcelain. Doesn't take much to crack one when a header bumps in to it on install.

 

i was doing my install and tried to rush it because it was getting dark. finally got it al done and was excited to go go test drive it and it ran like ****. when i got back i had two burnt wires and half the wires were not even pushed in all the way. in my mind i thought i checked everything. sometimes we get in a rush and forget things