Phil,

Im no expert on how to fix your emmissions problems but i can give you some info on your other questions. First, You may want to consider switching your platinums back to copper plugs. Do a search on this site under "platinum spark plugs" you will see why. Also, the small vacuum line you are referring to is a breather hose for your fuel pressure regulator. They attach the line to your valve cover breather hose to protect it from contamination and for emmissions purposes if the fuel press. reg. becomes faulty and leaks. I do believe high NOx is related to high exaust temps which can be caused by lean mixture.....I think, don't take my word for it.

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320