i just replaced all breather hoses i my 16v, the big one you guys mentioned had split, so had the inlet manifold pressure sensor hose(little hose at back of throttle body to ecu, this was causing lumpy running, poor mpg ect), i decided then to change all those small diameter hoses as a large length only cost me £1 at the local motor factors. the result is astounding, my car feels unbeleivable, better then it ever has and i have owned it for three years. by the way there are 4 such hoses
1) throttle body to ecu
2)throttle body to airbox
3)top of rocker cover
4)crank case breather box
Cannot recommened doing this enough