on my 1.3 mk2 astra i had the engine running with the air box off and there was i light smoke or steam coming from the larger of the two pipes connected to it (im sure this is the breather pipe). i took this pipe off totally and it seemed to run better than it had been. should the air from it be dirty? is it ok to have the pipe off?? whats the breather pipe actually do??
i presume its the one that comes from the top of the engine, out of a little raised section with OHC written on top ?? This is the cam housing breather and pipes the oil vapour and some minor escaping fuel vapour back into the carb. It reduces emmisions and increases mpg a bit. I wouldnt recommend venting this to the atmosphere cause you get sickly oil vapour coming into the car when you use the fan heater, gives you a bit of a dicky stomach.