diagnosing a check engine light on a 1999 C280 benz. failed smog (basic), found code P0170/173. Saw the same code on a 1999 E430 (replaced fuel filter) cleared codes, roadtest, concern solved. Not so with the C280. keep finding the same code. Tune up specs in good condition, no vaccum leaks, all o2's working normally. I Am stuck! Leaning toward possible partially restricted twc? Help! This is a sold unit!!!!