A Bad EGR valve or blocked up return pipe causes cars to run / idle badly. why then if you remove the EGR and use a block off plate does it run fine if all that does it block it up as if the EGR was bad or blocked. it makes no sense....please explain...
they sell block off plates for performace cars to get rid of teh useless EGR as it robs teh engine of power but helps with emmisions. i could care less if the world explodes but i want my car to run as good as possible (thats why i removed teh cats too 
) being stuck open vs stuck closed is a nice guess...but the pipe was blocked/clogged and so that a stuck closed thing...anyhow i guess from these answers unpluging the EGR from the ECU will help out.. thanks for the answers so far
Onboard computer, or ECC (electronic computer control) treats this as an air source, sort of like an intake, sort of like a vaccum. The valve reads flow from your exhaust (for utterly useless emissions reasons if you have a good running engine) so its treated like a controlled leak -- so when its plugged up, the onboard computer is expecting air and the engine starts to choke itself -- why? its expecting that extra bit of air flow, so there's too much gas or not enough. Now, if you remove it, the computer stays "Wait, I have no reading from the EGR (or the reading doesn't make any sense), I need to use a basic setting" and it does, simple as that. Usually, EGRs are just annoying, but rather cheap to replace.
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