This is only a theory, but as soon as I have some spare time tomorrow Ill have the EGR installed and tested for CEL.
Im gonna start with how the EGR valve and system work.
The EGR valve works in similar way like the BOV. It has vacuum diaphragm which attached to a valve and there is a spring which closes the valve when vacuum is missing.
http://i232.photobucket.com/albums/e...m12346/EGR.jpg
The valve is located between the exhaust recirculating inlet and the intake manifold inlet, and when a vacuum is applied it merges the two cambers which introduces exhaust gas to the intake manifold to reduce combustion temperatures and emissions.
EGR SYSTEM:
When the ECU closes the IAC and opens the EGR, it's looking for the intake manifold vacuum to suck enough air /exhaust gas/ to maintain idle through the exhaust recirculating hole on the EGR. You get a CEL when you block this /Ive tried this/, as you completely block the system off. When the ECU opens the EGR, the ECU sees the RPMs drop due to a blocked air /exhaust gas/ source.
To avoid the CELs, the EGR system has to be in working condition and all you really want to do is keep the engine from sucking "bad air" from the exhaust. So the the regular block off plate has to be modified to block off that exhaust outlet on the head while allowing the EGR system to still draw air.
So, drill a hole in one of the circles on the block off plate:
http://i232.photobucket.com/albums/e...6/DSC00134.jpg
Then locate the exhaust recirc. port on the EGR valve /usually on the bottom/ and drill a hole thru it:
http://i232.photobucket.com/albums/e...6/DSC00133.jpg
http://i232.photobucket.com/albums/e...6/DSC00132.jpg
Place the block off plate on top of the EGR so the hole is over the intake manifold port, and blocking the exhaust port.
http://i232.photobucket.com/albums/e...6/DSC00135.jpg
http://i232.photobucket.com/albums/e...6/DSC00136.jpg
Now bolt the EGR valve with the block off plate to the intake manifold and test drive it.
Ill have the results tomorrow morning