[Marcosis]

Hi all,
Im new here, ive got a 99 windstar w/ 85000mi, just replaced the steering rack, have abs light intermitently on, I already checked the sensors and im going to bleed the brakes this weekend. A couple of weeks ago I started hearing a valvetrain like knock, I scanned for codes and got 0720 output speed sensor, 0171, 0174 lean bank ind. I figured I would give the isolator bolt fix a whirl hoping the plenum is the culprit. well I got as far as pulling the intake bolts and the last one just spins, any ideas on how to get that little bugger out? While I was thinking about that I decided to pull the plugs. I think I found my knock problem. plugs 4,5,and 2 were all broken, the tops were just sitting inside the ceramic part, Im pretty sure I didnt break them taking them out, what would cause plugs to come apart like that they looked pretty scorched and beat up and would that cause an engine knock? Marc