To decrease the oxides of nitrogen emission, some of the exhaust gases are rerouted back into the EGR valve into the intake manifold to decrease combustion temperatures. In the units with carburetor, the EGR system consists in EGR valve, EGR vacuum modulator, and bi-metal vacuum switching valve (BVSV), with the EGR valve being controlled by the ported vacuum depending on the load. To avoid recirculation at idle, the vacuum signal is taken above the idle throttle position, and during start of the engine, the thermovalve opens and thus keeps the EGR valve closed. When the coolant temperature rises above the set temperature of the BVSV, it turns off and the ported vacuum engages the EGR valve through the EGR vacuum modulator which has an atmospheric bleed that is dependent on exhaust pressure. EGR is also used for fuel injected models and has the EGR valve, EGR modulator, vacuum switching valve (VSV), Electronic Control Module (ECM) and other sensors incorporated in a system where the ECM is set for optimum EGR valve lift under varying conditions. To check the EGR valve you need to push on the diaphragm to see if you have some kind of movement, then start your engine, then remove the vacuum hose and connect a hand vacuum pump to it; the vacuum reading should remain steady while your engine runs poorly. If the vacuum situation is in a state of insecurity or the engine operation is proper, then the EGR valve needs to be replaced or checked for obstruction. Regarding the EGR vacuum modulator valve, it should be removed, the filters should be inspected and cleaned and air should be able to pass through the valve. Extensive checks can be done only using special equipment so it is suggested to go to dealer's service center. In case of EGR removal, unbolt and pull out the EGR pipe joining and the mounting screws to pull out the EGR valve, examine if it is stuck or seasoned with carbon, and within the same procedure, the mounting of the EGR valve is done in the same process but in reverse. To assemble the EGR vacuum modulator remove and disconnect the vacuum hoses which should be labeled and then reverse the process.