I vacuum checked my EGR valve today - works good, I did find the EGR passage in my plenum was plugged up - I cleaned it out and I didn't hear any rattling on the hills when I came home from work so maybe that's all that was wrong. I'll try cleaning the mass air sensor tommorow. Where is the knock sensor? My Haynes book talks about it but it doesn't tell you where it's located? I'll also check the EGR canister purge operation and differential pressure feedback (DPFE) sensor tommorow. I didn't hear or see any signs of a crack in the EGR tube - but I'll look closer tommorow.