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It's part of the secondary air system which help reduce cold-start emissions when the CAT is still warming up. It feeds air from the air cleaner into additional pipework on the exhaust mani and mixes with the exhaust gases, which apparently raises the temp of the exhaust and helps burn pollutants as well as help bring the CAT up to operational temp more quickly. Once the coolant temp is up and the CAT is working properly, the system is switched off by the ECU...that's what it says here anyway.
I guess it won't affect performance much, if at all, just means your emissions will be a bit high until the motor is warmed up.![]()
My old LC used to do this and the noise was exactly as decribed earlier a vacuum cleaner and it only lasts a minute and then switches off. The thing is I read a thread on here and one of the lads posted some pictures. Basically there is a leak coming from the secondary air pump which can be fixed but for it to be quite lous means the leak is getting big. Do a search and you will find details.
jay
Mine does this too, sounds like the airbox is missing for about a minute then a psssst and dead silent, did anyone find the thread about fixing it then, ive searched too but no joy cheers all.![]()