2. A simple visual inspection can be performed, but this requires removing the external air duct.
3. Locate the vacuum valve in the air cleaner assembly. It is located inside the air filter duct pipe where you removed the outer duct. Make sure the flexible intake tube under the air filter is securely fastened and not damaged.
4. The check should be performed with the engine cold and the ambient temperature low (less than 18°C). Start the engine and look through the air duct tube at the valve (which should move to the "warm" position). When the valve is raised, air cannot pass through the end of the air duct tube, but instead enters the air filter through the intake attached to the exhaust manifold. If you can't see into the ductwork, you may need a mirror.
5. When the engine has warmed up to operating temperature, the valve should drop to the "heat off" position to allow air to pass through the air duct (see illustration). Depending on the outside temperature, this may take 10 to 15 minutes. To speed up the test, you can connect an external air duct, take it for a short drive, and then check to see if the valve has dropped.
28.5. Air thermostat valve (indicated by the arrow) located in the air filter air duct pipe (in this case it is in the lowered position)
6. If the air filter is not working properly, information on further action is contained in chapter 6.