Well it all started when I was trying to fix my idleing issues today. I was about a block away from my house and decided to look at a few things under the hood. I pulled vacuum line off of the EGR valve and noticed that it would only start sucking when givin throttle so I switched it with a line that was sucking in air all the time. Well it seemed to idle alittle bit better so I start driving it and hear the dreaded knocking noise from my motor, I quikly pull over and switch the vacuum lines back how they were, but its still knocking. I limp it home and shut it down, well 5 minutes later I start it up to see if I can pinpoint where the knocking is coming from, but it was'nt knocking after I started it. I ran a compression check and when I got to Cylinder #8 I found a crushed spark plug, changed that and it runs fine now. Im assuming it didnt hurt any valves seeing as the compression on all 8 cylinders matched. My question is that, what caused this? Im assuming if it was a streched piston or something it would keep knocking. Did messing with the EGR valve somehow throw my timing/or computer way off?