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The Curious Bag
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The EGR (Exhaust Gas Recirculation) system was first introduced in the early 1970s as stop-gap means of reducing emissions and continues in use today, albeit in a less vital capacity.
EGR Purpose
An EGR system siphons off a little bit off exhaust gas and feeds it into the intake system via a vacuum-controlled EGR valve.
EGR Function
By introducing a little bit of exhaust gas into the system, an EGR is intended to reduce cylinder combustion temperatures below the 2,500 degrees F at which toxic oxides of nitrogen (NOX) emissions form.
Warming Effects
In addition to cooling cylinder temperatures, the EGR valve often opens when the engine is cold. This increases the temperature of the incoming air-stream and helps a cold engine run more efficiently.
Valve Failure
EGR valves can become clogged by carbon over time and stick open or closed. This will cause poor idle quality and hesitation.
Valve Identification
The EGR valve is almost always attached to the intake manifold by two or three bolts and has a 2 to 3 inch diameter diaphragm on top. There will be either a rubber vacuum hose or a wiring harness protruding from the middle of the round diaphragm.
Source:
Obd-codes.com: EGR Valve Explained
Faqs.org: Function of an EGR Valve
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