Examination
1. On C16 NZ, C16 NZ2 and C18 NZ engines, it is recommended to check the system annually by monitoring the movement of the valve diaphragm mounting plate as follows. Note that the mounting plate is only visible through openings in the back of the valve, so a flashlight and a small mirror may be required. On X16 SZ engines, special Opel test equipment must be used to test the exhaust gas recirculation system.
2. Warm up the engine to normal operating temperature, set the idle speed by briefly opening and closing the throttle. The mounting plate must move upwards as the manifold vacuum changes. When the engine returns to idle smoothly, push the mounting plate up (do this very carefully so as not to deform it or damage the diaphragm). The idle speed should drop noticeably (approximately 100 rpm).
3. If the valve does not work as described, it must be cleaned.
Removing
4. Disconnect the hose from the valve, then unscrew and remove the valve (see illustrations). Clean it of carbon deposits with a wire brush, but do not damage the valve seat. Replace gasket.
Installation
5. Install the valve, connect the hose, then check the operation of the system; if there is no improvement, the valve must be replaced.
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