PO401 EGR Valve SES light problems...

Hi everyone. We bought a 1998 Grand Prix SE, 3.1L a few weeks ago and the SES light has been on since. The code we're getting is PO401 EGR Valve Insufficient Air Flow. We have:

1.) Replaced the EGR valve. Twice.
2.) Cleaned out the tube that clogs with carbon. No carbon, air seems to be fllowing fine.
3.) PCV valve and gasket.
4.) MAP sensor.

We replace the part and have the code reset with the computer and the light stays off for about 25-30 miles and then it comes back on over and over again like clockwork. We are driving around with a REJECT sticker sonce this problem caused us to fail emissions. We've also tried SeaFoam to no avail.

The car does seem to hesitate sometimes with acceleration. We are truly at our wit's end with this one. We bought another car so we wouldn't have to deal with the headaches from our other car, a 1995 Mitsubishi Galant, but thus far, the Grand Prix has driven us insane!

Can anyone please tell me what else we should possibly try? It's like an insane mystery!

Many thanks in advance!

did you use an aftermarket or AC Delco EGR valve? Check the MAP sensor vacuum lines to see if any are cracked. A bad vacuum signal to the MAP can trip a P0401 code.

The EGR is an aftermarket part from AutoZone (I think it's a Wells). The vacuum lines have been checked and there is no problem with any of them. We just don't even know what else to check now...

Thanks for your reply!

Are you sure its an aftermarket?? Cuz I'm pretty sure the only one they sold there was O.E.M

May need another EGR gasket.

I checked AutoZone again and the part is indeed an OEM part. But we replaced the EGR gasket as well and it is still coming up with the PO401 code. We are taking the car for a Diagnostic tomorrow so hopefully they will figure out what the hell is wrong before I lose my mind!

Is there supposed to be any lubrication between the pindles and the coils on the EGR valve? I noticed when I changed mine that neither the old one nor the new (used) one had any lubrication in this area. What I did notice was condensation forming below the EGR valve.. it seems like a bad combination.