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EGR, or Exhaust Gas Recirculation, reduces NOx of the exhaust emission by recirculating some of the engine's exhaust back into the intake manifold. Its purpose is to lower combustion temperature and reduce emissions. Usually, this is done at lower rpm example is cruising or in a traffic jam. It was reported that it leads to carbon build-up inside the engine if a particular operation temperature isn't reached. Talk to your local mechanic on how to prevent any build-up.

  • The EGR system includes a passage between the exhaust manifold and intake manifold. The EGR valve opens and closes the passage. Most of the EGR valves have a spring-loaded diaphragm the help in forming a vacuum chamber that is located at the top of the valve. The chamber links a tube to a vacuum port in the throttle body. When there is no vacuum at this port, the spring pushes the diaphragm down and keeps the passage closes. 

As the throttle valve opens, it moves from the vacuum port. The intake manifold vacuum now acts through the port and pulls the diaphragm up, enabling the valve to open. Some of the exhaust gas is flowing through the valve into the intake manifold. During a wide-open throttle condition, the intake manifold vacuum is low and the EGR valve will close. The combustion is over more quickly and the nitrogen oxide has less time to form.