NOx emissions are reduced by the EGA system, which recirculates exhaust gas back to the intake manifold. Venturi Vacuum Control, as well as Ported Vacuum Control, is mostly used by carbureted engines. Poppet valves, tapered stem valves and integral backpressure valves are some of the different types of EGA valves. A few models are equipped with a Coolant Spark Control system. Testing EGR valve movement, inspecting hoses and troubleshooting problems are part of checks. Other steps include valve travel assessment, deposits cleaning and vacuum amplifier inspection. Dual EGA solenoid valve checks involve solenoid resistance, hoses, and voltage verification.