The purpose of butter fly valve is to maintain one way opening during induction stroke and exhaust stroke.
An airbox is a chamber in a car or motorcycle engine which draws in air and distributes it to the carburetors.
In the bottom half of the airbox.
Reattaching it to your airbox (with the filter) or the engine? And which year and what size engine?
engine
There's a hose that runs from the top of the engine/transmission to the airbox. This is the Crankcase vent hose. Pressure in the crankcase caused by blowby is relieved into the airbox to reduce pollution. It's 100% normal for there to by oil in the bottom of the airbox Running the engine for long periods of time above 8,000RPM will increase the amount of oil in the airbox. There's a little drain hose on the bottom of the airbox, just pull the plug and let the oil drain out into the pan everytime you do an oil change.
The PCV system is not pulling in fresh air to the engine.
petrol-underneath on the front of the engine diesel- ontop, on the right hand side between the engine and airbox
look for the yellow top dipstick on the back left of the engine just behind and below the airbox (filter) (passenger compartment side). You do not have to remove the airbox.
Between the Airbox (where your filter is), and where it enters the engine.
there is an o2 sensor in the engine bay behind the engine by the firewall. its under the black airbox where the air filter is. its in between the catalyctic converter and manifold. right on the pipe. you cant miss it. easy to change yourself. just take the airbox out and its simple!
First off, open your hood and remove the airbox (this is assuming you have the 4 cylinder engine). Once you remove the airbox, look down at the rear of the engine and find the exhaust pipe. The oxygen sensor will be a few inches down the pipe from the exhaust manifold.
There will always be some oil in the intercooler. Part of the emissions system connects the engine breather to the airbox. As the turbo sucks air through the airbox it tends to suck some oil into the intercooler.