The EGR system consists of an EGR valve that regulates the flow of exhaust gases, as well as various vacuum and electrical control devices that prevent untimely operation of the EGR system. There is no need for EGR when the engine has a low enough temperature to reduce the ignition temperature in the engine. The use of RVG in this case would lead to unstable engine operation, therefore the RVG function is disabled by means of either a thermal valve or a fuel injection computer (controlling the coolant temperature). In addition, the EGR is also switched off at idle speed on a warm engine to prevent unstable speed or "jerking" when pressing the accelerator (gas) pedal.
A decrease in combustion temperature also leads to some reduction in power. Because of this, when the engine switches to the fully open throttle driving mode, the EGR function is disabled. Usually, the vacuum acting on the EGR valve overcomes the tension force of the spring inside the valve and holds it open. When the throttle valve is fully open, the vacuum acting on the EGR decreases and the spring closes the valve. A common symptom of a faulty EGR is a slight engine knock when the throttle is partially open, most noticeable under load, i.e. when climbing a hill or when carrying several passengers. The EGR valve can cause unstable and uneven idle speed. If the engine is adjusted correctly, and other reasons (vacuum leak, poor spark plug wires) eliminated, then if unstable idle speed appears, the fault lies in the EGR.
Examination
With the engine cool, disconnect the throttle body vacuum hose. Connect the hose to the vacuum pump.
Plug the branch pipe from which the hose was removed. Start the engine and try to create a vacuum using the hand pump. The EGR system will not maintain vacuum when the engine is cold and idling.
Warm up the engine to normal operating temperature. Before checking, the coolant temperature should be 80-85°C. Using a pump, create a vacuum of 30-43 mm Hg. The EGR system on the fuel engine should maintain a vacuum, while idling will not be accompanied by noticeable changes.
Allow the warm engine to idle as described above. Create a vacuum of 83 mm Hg and listen to the engine running. When the required degree of vacuum is reached, the idle speed will become unstable, uneven, the engine may even stall as soon as the EGR valve opens and lets the exhaust gas through. The system must maintain a vacuum with the valve open.