Some 49 state, and many California emission equipped Passat and A4 Vehicles sold in the USA are equipped with an EGR valve. To reduce oxides of nitrogen (NOx) emissions, metered amounts of exhaust gases are added to the air/fuel mixture to lower combustion temperatures during combustion.
The vacuum-operated EGR valve controls the volume of exhaust gas flow into the intake manifold. Vacuum for the valve is controlled by coolant temperature to prevent the valve from operating during the engine's warm up period. The EGR valve should be closed whenever the engine is cold, and closed at all operating temperatures when the engine is idling or at full throttle. Once the engine has reached normal operating temperature, the valve is partially opened just above idle and fully open during mid range throttle operation.
To check the operation of the Exhaust Gas Recirculation (EGR) valve proceed as follows:
- Inspect the vacuum lines and intake manifold-to-cylinder head connections making sure there are no leaks, and the vacuum lines are not plugged or bent.
- With the engine cold, start the engine and allow it to idle.
- While the engine idles, connect a hand vacuum pump to the EGR valve and draw a vacuum. The engine should idle rough or even stall. This indicates the valve is opening and closing fully.
- Reconnect the vacuum hose to the EGR valve, disconnect the vacuum supply hose at the thermoswitch and connect the hand pump. Draw a vacuum to make sure the thermoswitch operates. If the engine is cold, (below 120°F or 49°C), the idle should not change. If the coolant temperature is above about 120°F (49°C), the thermoswitch should open and allow vacuum to the EGR valve and the engine should idle rough or even stall.
- If equipped, to test the vacuum amplifier, connect a tee fitting and vacuum gauge or mercury column to the amplifier input hose, between the throttle body and the amplifier. At idle, there should be about 0.3 inches (7.6mm) (Hg) vacuum.
- Tee the gauge into the amplifier output hose, between the amplifier and the thermoswitch. At idle there should be about 1.9-3.5 inches (48.2-88.9 mm) (Hg) of vacuum.
- Remove the negative battery cable.
- Disconnect the vacuum hose from the EGR valve.
- Unbolt the EGR line fitting on the opposite side of the valve.
- Remove the 2 retaining bolts.
- Lift the EGR valve from the intake manifold.
- Installation is the reverse of removal. Use new gaskets and tighten the bolts to 84 inch lbs. (10 Nm).