97 lsi PO400 code problem

[eddierotary]

im been haing problem with my car in the last few months, im been getting this po400 code wich is egr code, idk why. this is what i have done so far,

i cleaned the egr ports on the intake
check the tube and is ok, exhaust go thru it
the egr valve works, holds vaccum
replaced and cleaned all the vaccum lines
check the wires to the solenoid and they are good
and replaced the solenoid

so what else can cause it? what else i should look for?
thanks
eddie

[r3v_v3ng3]

you should go to literatures and manual and download the FSM for your car. There should be a step by step on trouble shooting your egr

[L.Michael]

Did you check the working state of the EGR? Its simple, you just gotta get a finger or 2 underneath where the diaphragm is, and push up. You should get a decrease in RPM's.