Vehicles sold in some parts of the U.S. with Motronic fuel injection 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 and supplied through a vacuum amplifier. The EGR valve is closed when the engine is cold or at idle or full throttle. The valve is partially open just above idle and fully open at mid throttle settings.
- While idling the engine, 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, 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.
- 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 (Hg) of vacuum.
REMOVAL & INSTALLATION
- 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 two retaining bolts.
- Lift the EGR valve from the intake manifold.
- Installation is the reverse of removal. Use new gaskets and tighten the bolts to 7 ft. lbs. (10 Nm).