Didn't read all replies. To the OP,it seems like maybe you're confusing EGR (exhaust gas recirculation) with a restrictive muffler (exhaust gas restriction). EGRs do not restrict exhaust flow. They simply divert some exhaust gas back into the intake stream at certain times. They are used as a tool in meeting emission and CAFE mileage requirements. The exhaust gas is theoretically inert. If it's inert, it will not support any combustion process. By partially filling the cylinder with inert gas, the amount of fuel required to maintain stoich is reduced. Power is reduced also, as is heat due to a smaller than normal combustion event. If the the same amount of fuel that is supplied while the EGR is commanded on were supplied during a non EGR combustion cycle, the a/f ratio would be very lean, thus causing NOx to rise. Likewise, if an EGR is commanded on manually, and the fuel rate does not change, the engine will stumble and run very rough, even possibly stall st idle due to an excessively rich mixture created by lack of oxygen. An exhaust restriction will typically create excessive heat in any application unless it's restricted to the point it won't run well enough to even produce a lot of heat.
EGRs theoretically reduce the displacement of the engine when commanded on. They're not used at idle or other high load situations unless cyl head temps rise too high and the pcm determines it needed to help cool the engine. There are a ton of different style of EGR systems and the newer systems seem to be less intrusive and actually work, for awhile. But, most all have one thing in common, over time they carbon up and cause people grief.
