1998 Chevy Lumina has check Engine light on and code says egr valve which has been replaced now what

Here is a list of possible causes. Some things you have already done.

EGR solenoid valve harness is open or shorted
- EGR solenoid valve circuit poor electrical connection
- EGR volume control valve stuck closed
- Faulty EGR Pressure sensor
- Faulty EGR temperature sensor and circuit
- Faulty EGR Valve
- EGR passage clogged
- Exhaust gas leaks
Read more: http://engine-codes.com/p0401_ford.html#ixzz28fATCih2

It should go off after the diagnostic test from the on board computer cycles through 2-3 times without any error. An alternative is to take it to Autozone and have them clear the code for you. They will do this for free and then you can see if the code comes back

Follow the link for help with this fault code P1405 Ford DPF EGR Sensor Circuit High Voltage Detected

I suggest you replace the EGR valve position sensor.

Which engine ? Antifreeze can cause the milky look if it got into the intake or exhaust and drawn into the EGR .

Could be a clog in the tube going to the EGR valve, or in the tube/hose leading away from it!

high pitch whine- like a whistle? check for a plugged egr valve or a melted catalytic converter

Could be a EGR vacuum issue or temp sensor issue

Common Problems That Trigger the P0401 Code

• Restriction in the EGR passages, usually caused by carbon buildup
• Lack of a proper vacuum signal to the EGR Valve from EGR Vacuum Solenoid
  
• EGR Vacuum Modulator is defective
• EGR Temperature Sensor is defective
• EGR Valve is defective

This is from:
http://repairpal.com/OBD-II-Code-P0401-Ford

Well, the po401 is saying is that the egr valve has restricted flow. After changing the egr and the tube, something else is causing the restriction. a more thorough diagnosis is recommended. The po420 code sounds like a possible catalyst failure or an o2 sensor failure.

when a code is set for something it doesnt mean replace it, Egr system has an evr solonid that controlls the egr, There is rubber hoses that run between them some are plastic and break, Id have the hose checked and if its good replace evr solenoid

You could have a restriction in the egr ports. remove the valve. Plug the holes, start engine. 1 hole will be blowing out exhaust, the other will have large vacuum.