EGR solenoids are used to switch engine vacuum on and off at the right time. The time is based strictly on engine load and temperature. If the EGR circuit activates too soon, the engine will miss and run badly, or not at all. If it is defective and does not switch on at all, the engine will ping and rattle under a load or going uphill. It's important that the EGR solenoid be in proper working order.
Remove the EGR solenoid from the vehicle. This is usually done by removing one attachment nut. Unplug the connector.
Make a jumper wire with an in-line fuse holder and install a 10-amp fuse. Crimp each end of the fuse holder to a section of wire using crimp connectors. Make another jumper wire and attach both wires to the connectors on the solenoid. Be careful not to let the wires touch or the fuse will blow when the other ends of the wire are attached to the positive and negative battery post. The solenoid should click as it is powered by the battery.
Remove one of the jumper wires from the battery and install vacuum hoses on the two vacuum ports located on the EGR solenoid. The solenoid controls a rapid-deployment valve to regulate the flow of vacuum, through the ports, to the EGR valve. Blow forcefully through one of the hoses. Air should not pass through. If air cannot pass through, neither can vacuum and the valve is closing properly.
Attach the loose jumper wire back on the battery. The solenoid should click again. Blow through the vacuum hose. Air should pass through when it is energised. This test determines whether the valve is opening when it is energised, allowing unrestricted flow of vacuum. If the solenoid fails any of these tests, replace it.
Some solenoids were designed to modulate the vacuum to the EGR valve. They open and close tens of thousands of times. They were primarily used on older models and failed often.